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• Is my implementation of A* wrong?

  - by Bloodyaugust

  I've implemented the A* algorithm in my program. However, it would seem to be functioning incorrectly at times. Below is a screenshot of one such time. The obviously shorter line is to go immediately right at the second to last row. Instead, they move down, around the tower, and continue to their destination (bottom right from top left). Below is my actual code implementation: nodeMap.prototype.findPath = function(p1, p2) { var openList = []; var closedList = []; var nodes = this.nodes; for (var i = 0; i < nodes.length; i++) { //reset heuristics and parents for nodes var curNode = nodes[i]; curNode.f = 0; curNode.g = 0; curNode.h = 0; curNode.parent = null; if (curNode.pathable === false) { closedList.push(curNode); } } openList.push(this.getNode(p1)); while(openList.length > 0) { // Grab the lowest f(x) to process next var lowInd = 0; for(i=0; i<openList.length; i++) { if(openList[i].f < openList[lowInd].f) { lowInd = i; } } var currentNode = openList[lowInd]; if (currentNode === this.getNode(p2)) { var curr = currentNode; var ret = []; while(curr.parent) { ret.push(curr); curr = curr.parent; } return ret.reverse(); } closedList.push(currentNode); for (i = 0; i < openList.length; i++) { //remove currentNode from openList if (openList[i] === currentNode) { openList.splice(i, 1); break; } } for (i = 0; i < currentNode.neighbors.length; i++) { if(closedList.indexOf(currentNode.neighbors[i]) !== -1 ) { continue; } if (currentNode.neighbors[i].isPathable === false) { closedList.push(currentNode.neighbors[i]); continue; } var gScore = currentNode.g + 1; // 1 is the distance from a node to it's neighbor var gScoreIsBest = false; if (openList.indexOf(currentNode.neighbors[i]) === -1) { //save g, h, and f then save the current parent gScoreIsBest = true; currentNode.neighbors[i].h = currentNode.neighbors[i].heuristic(this.getNode(p2)); openList.push(currentNode.neighbors[i]); } else if (gScore < currentNode.neighbors[i].g) { //current g better than previous g gScoreIsBest = true; } if (gScoreIsBest) { currentNode.neighbors[i].parent = currentNode; currentNode.neighbors[i].g = gScore; currentNode.neighbors[i].f = currentNode.neighbors[i].g + currentNode.neighbors[i].h; } } } return false; } Towers block pathability. Is there perhaps something I am missing here, or does A* not always find the shortest path in a situation such as this? Thanks in advance for any help.

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• Multidimensional multiple-choice knapsack problem: find a feasible solution

  - by Onheiron

  My assignment is to use local search heuristics to solve the Multidimensional multiple-choice knapsack problem, but to do so I first need to find a feasible solution to start with. Here is an example problem with what I tried so far. Problem R1 R2 R3 RESOUCES : 8 8 8 GROUPS: G1: 11.0 3 2 2 12.0 1 1 3 G2: 20.0 1 1 3 5.0 2 3 2 G3: 10.0 2 2 3 30.0 1 1 3 Sorting strategies To find a starting feasible solution for my local search I decided to ignore maximization of gains and just try to fit the resources requirements. I decided to sort the choices (strategies) in each group by comparing their "distance" from the multidimensional space origin, thus calculating SQRT(R1^2 + R2^2 + ... + RN^2). I felt like this was a keen solution as it somehow privileged those choices with resouce usages closer to each other (e.g. R1:2 R2:2 R3:2 < R1:1 R2:2 R3:3) even if the total sum is the same. Doing so and selecting the best choice from each group proved sufficent to find a feasible solution for many[30] different benchmark problems, but of course I knew it was just luck. So I came up with the problem presented above which sorts like this: R1 R2 R3 RESOUCES : 8 8 8 GROUPS: G1: 12.0 1 1 3 < select this 11.0 3 2 2 G2: 20.0 1 1 3 < select this 5.0 2 3 2 G3: 30.0 1 1 3 < select this 10.0 2 2 3 And it is not feasible because the resources consmption is R1:3, R2:3, R3:9. The easy solution is to pick one of the second best choices in group 1 or 2, so I'll need some kind of iteration (local search[?]) to find the starting feasible solution for my local search solution. Here are the options I came up with Option 1: iterate choices I tried to find a way to iterate all the choices with a specific order, something like G1 G2 G3 1 1 1 2 1 1 1 2 1 1 1 2 2 2 1 ... believeng that feasible solutions won't be that far away from the unfeasible one I start with and thus the number of iterations will keep quite low. Does this make any sense? If yes, how can I iterate the choices (grouped combinations) of each group keeping "as near as possibile" to the previous iteration? Option 2: Change the comparation term I tried to think how to find a better variable to sort the choices on. I thought at a measure of how "precious" a resource is based on supply and demand, so that an higer demand of a more precious resource will push you down the list, but this didn't help at all. Also I thought there probably isn't gonna be such a comparsion variable which assures me a feasible solution at first strike. I there such a variable? If not, is there a better sorting criteria anyways? Option 3: implement any known sub-optimal fast solving algorithm Unfortunately I could not find any of such algorithms online. Any suggestion?

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• The long road to bug-free software

  - by Tony Davis

  The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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• I need help with 2D collision response (of stacking rotating polygons, with friction and gravity, for a game)

  - by Register Sole

  Hi I am looking for suggestions on how to write a collision response for game programming purpose (so not a scientific simulation). I am dealing with 2D polygons that are rotating, and I want them to be able to stack. I also want friction and gravity. I have a detection mechanism that returns the separating axis, how long the polygons are overlapping, and up to 2 points of contact. For the response, I am currently using an impulse-based response, which main idea is: find the separating axis, length of overlap, and the point of contact (if there are two, pick a random point between to simulate averaged force. i believe there are better ways than this) separate the object (modifying their positions, taking into account of their masses. i do not separate them completely though, to keep track that they are colliding to reduce jitter) calculate normal force based on the coefficient of restitution as if there is no friction. calculate friction, as if there is no normal force. I also assume that the direction of the friction is the same throughout the collision. apply the two forces (which result in a rather inaccurate result, since each force is calculated as if the other is not present. for non-rotating bodies though, this method is exact) I am aware that this method requires the coefficient of friction to be sufficiently small due to the assumption that the direction of friction stays the same in a collision. Also, the result is visually satisfying if gravity is not present. However, when there is gravity, objects on ground jitter and drift (even with zero coefficient of restitution)! It also happens for stacking objects. Larger coefficient of restitution and gravity increase the jittering. I hope you can help me with this. Some things i would like to know more about is how to handle collision with two point of contacts (how to end up having an object sitting still on the ground?), how to reduce, and prevent if possible, jitter and drift (do people use the most accurate method possible, or is there a trick to overcome this?), and how to handle multiple objects collision (for example, in the case of stacking objects, how do I check collisions between all of them and keep them all stable at every frame so they don't jitter?). A total reformulation of my algorithm is also welcomed, as long as it works. Another thing to note is that I am not making a Physics game, so I only need a visually satisfying response (though a realistic response is preferable, if it is not performance-heavy). But surely jittering and drifting objects on flat ground are not at all acceptable. In addition, I am a Physics student, so feel free to talk about impulse and whatever needed. Finally, I'm sorry for the long post. I tried to be as concise as I can. Thank you for reading it! EDIT It seems what I didn't manage to come up all this time is to separate resting contact as a class of its own and how to solve them. Currently reading the paper suggested by Jedediah. More suggestions on the topic are welcome :) CASE CLOSED After reading various papers referenced in the paper, successfully implemented simultaneous impulse method (referring to the original paper by Erin Catto, [Catt05]). Thanks maaaan!! The paper is wonderful. The current system is visibly much better than the previous. Still haven't separated resting contact as a class of its own though, which brings me to my next question. Love you all! Haha (sorry, I'm just so happy thanks to you).

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• I thought the new AUTO_SAMPLE_SIZE in Oracle Database 11g looked at all the rows in a table so why do I see a very small sample size on some tables?

  - by Maria Colgan

  I recently got asked this question and thought it was worth a quick blog post to explain in a little more detail what is going on with the new AUTO_SAMPLE_SIZE in Oracle Database 11g and what you should expect to see in the dictionary views. Let’s take the SH.CUSTOMERS table as an example.  There are 55,500 rows in the SH.CUSTOMERS tables. If we gather statistics on the SH.CUSTOMERS using the new AUTO_SAMPLE_SIZE but without collecting histogram we can check what sample size was used by looking in the USER_TABLES and USER_TAB_COL_STATISTICS dictionary views. The sample sized shown in the USER_TABLES is 55,500 rows or the entire table as expected. In USER_TAB_COL_STATISTICS most columns show 55,500 rows as the sample size except for four columns (CUST_SRC_ID, CUST_EFF_TO, CUST_MARTIAL_STATUS, CUST_INCOME_LEVEL ). The CUST_SRC_ID and CUST_EFF_TO columns have no sample size listed because there are only NULL values in these columns and the statistics gathering procedure skips NULL values. The CUST_MARTIAL_STATUS (38,072) and the CUST_INCOME_LEVEL (55,459) columns show less than 55,500 rows as their sample size because of the presence of NULL values in these columns. In the SH.CUSTOMERS table 17,428 rows have a NULL as the value for CUST_MARTIAL_STATUS column (17428+38072 = 55500), while 41 rows have a NULL values for the CUST_INCOME_LEVEL column (41+55459 = 55500). So we can confirm that the new AUTO_SAMPLE_SIZE algorithm will use all non-NULL values when gathering basic table and column level statistics. Now we have clear understanding of what sample size to expect lets include histogram creation as part of the statistics gathering. Again we can look in the USER_TABLES and USER_TAB_COL_STATISTICS dictionary views to find the sample size used. The sample size seen in USER_TABLES is 55,500 rows but if we look at the column statistics we see that it is same as in previous case except  for columns  CUST_POSTAL_CODE and  CUST_CITY_ID. You will also notice that these columns now have histograms created on them. The sample size shown for these columns is not the sample size used to gather the basic column statistics. AUTO_SAMPLE_SIZE still uses all the rows in the table - the NULL rows to gather the basic column statistics (55,500 rows in this case). The size shown is the sample size used to create the histogram on the column. When we create a histogram we try to build it on a sample that has approximately 5,500 non-null values for the column.  Typically all of the histograms required for a table are built from the same sample. In our example the histograms created on CUST_POSTAL_CODE and the CUST_CITY_ID were built on a single sample of ~5,500 (5,450 rows) as these columns contained only non-null values. However, if one or more of the columns that requires a histogram has null values then the sample size maybe increased in order to achieve a sample of 5,500 non-null values for those columns. n addition, if the difference between the number of nulls in the columns varies greatly, we may create multiple samples, one for the columns that have a low number of null values and one for the columns with a high number of null values.  This scheme enables us to get close to 5,500 non-null values for each column. +Maria Colgan

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• find substring and indices in mips

  - by ccc

  im trying find out substring and first occurrence indices. but something wrong. im comparing each element of pattern array and each element of string array until pointer reach to '\0'. and if any characater found it keep in temp array. and increasing pointers +1. whats the problem. algorithm is totaly wrong ? #Note: $v0 is a symbolic name used by the assember for $2. # $a0 is a symbolic name used by the assember for $4. .data prompt_str: .asciiz "Please type a text string: " prompt_ptr: .asciiz "Please type a pattern string: " print_yes: .asciiz "Yes, there is a match." print_no: .asciiz "No, there is no match." text_str: .asciiz "Text string : " pattern_str: .asciiz "Pattern string : " print_out: .asciiz "Output to be produced :" print_dash: .asciiz "----------------------" print_index: .asciiz "Starting index :" print_msg : .asciiz "Length of longest partial match = " nl: .asciiz "\n" str : .space 81 ptr : .space 81 tmp : .space 81 .text main: la $a0, prompt_str li $v0, 4 #print_string command. syscall la $a0,str #read string li $a1,81 li $v0,8 syscall la $t0,str #move string to $t0 la $a0,prompt_ptr li $v0,4 #print pattern command syscall la $a0,ptr #read pattern li $a1,81 li $v0,8 syscall la $t1,ptr #move pattern to $t1 la $t5,tmp #move temp to $t5 lb $t2,0($t0) #pointer first element array of string lb $t3,0($t1) #pointer first element array of pattern lb $t6,0($t5) #pointer first element array of temp loop : beq $t3,$0,end_loop beq $t2,$t3,match addiu $t0,$t0,1 j loop match : move $t6,$t2 addiu $t5,$t5,1 addiu $t0,$t0,1 addiu $t1,$t1,1 j print_match print_match : la $a0,text_str #print string li $v0,4 syscall move $a0,$t0 li $v0,4 syscall la $a0,nl #print newline character li $v0,4 syscall la $a0,pattern_str #print pattern string li $v0,4 syscall move $a0,$t1 li $v0,4 syscall la $a0,nl #print newline character li $v0,4 syscall la $a0,print_out #print output line and newline character li $v0,4 syscall la $a0,nl li $v0,4 syscall la $a0,print_dash li $v0,4 syscall la $a0,print_yes li $v0,4 syscall la $a0,print_index #print starting index li $v0,4 syscall li $v0,10 syscall end_loop : li $v0,10 syscall

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• Android: Autoscrolling HorizontalScrollView

  - by DroidIn.net

  I'm using the following code to simulate tabs and since there are more tabs that width can accommodate user can scroll left or right to make a tab button visible. It all works, however I also provide user with ability to fling between tabs by swiping finger left or right on the tab contents. Again - it works. But when I fling to the rightmost tab its corresponding button is barely visible. I want to autoscroll table inside the HorizontalScrollView so the selected tab button will be visible but when I execute HorizontalScrollView.smoothScrollTo(300, 0) nothing happens. It doen't matter how high I set first x parameter nothing will ever move (yes I do have an algorithm to calculate exact position). Here's XML code for scrolling tab buttons <HorizontalScrollView android:layout_width="fill_parent" android:background="@color/tabs_header" android:layout_height="55dip" android:scrollbars="none" android:id="@+id/tabsButtonView"> <TableLayout android:id="@+id/TableLayout01" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TableRow android:id="@+id/TableRow01" android:layout_width="fill_parent" android:layout_weight="1" android:layout_height="0dip" android:paddingTop="5dip" android:paddingLeft="3dip"> <ImageButton android:src="@drawable/linkup_logo_small" android:id="@+id/tabBtt0" android:layout_width="wrap_content" android:layout_marginLeft="2dip" android:layout_marginRight="2dip" android:layout_height="fill_parent" android:padding="5dip" android:background="@drawable/tab_selected"></ImageButton> <ImageButton android:src="@drawable/simplyhired_small" android:id="@+id/tabBtt1" android:layout_height="fill_parent" android:layout_width="fill_parent" android:layout_marginLeft="2dip" android:layout_marginRight="2dip" android:padding="5dip" android:background="@drawable/tab_normal"></ImageButton> <ImageButton android:src="@drawable/indeedcom_small" android:id="@+id/tabBtt2" android:layout_width="fill_parent" android:layout_height="fill_parent" android:padding="5dip" android:layout_marginLeft="2dip" android:layout_marginRight="2dip" android:background="@drawable/tab_normal"></ImageButton> <ImageButton android:src="@drawable/careerbuilder_logo_small" android:id="@+id/tabBtt3" android:layout_width="fill_parent" android:layout_height="fill_parent" android:padding="5dip" android:layout_marginLeft="2dip" android:layout_marginRight="2dip" android:background="@drawable/tab_normal"></ImageButton> </TableRow> </TableLayout> </HorizontalScrollView>

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• Optimizing transition/movement smoothness for a 2D flash game.

  - by Tom

  Update 6: Fenomenas suggested me to re-create everything as simple as possible. I had my doubts that this would make any difference as the algorithm remains the same, and performance did not seem to be the issue. Anyway, it was the only suggestion I got so here it is: 30 FPS: http://www.feedpostal.com/test/simple/30/SimpleMovement.html 40 FPS: http://www.feedpostal.com/test/simple/40/SimpleMovement.html 60 FPS: http://www.feedpostal.com/test/simple/60/SimpleMovement.html 100 FPS: http://www.feedpostal.com/test/simple/100/SimpleMovement.html The code: package { import flash.display.Sprite; import flash.events.Event; import flash.events.KeyboardEvent; import flash.utils.getTimer; [SWF(width="800", height="600", frameRate="40", backgroundColor="#000000")] public class SimpleMovement extends Sprite { private static const TURNING_SPEED:uint = 180; private static const MOVEMENT_SPEED:uint = 400; private static const RADIAN_DIVIDE:Number = Math.PI/180; private var playerObject:Sprite; private var shipContainer:Sprite; private var moving:Boolean = false; private var turningMode:uint = 0; private var movementTimestamp:Number = getTimer(); private var turningTimestamp:Number = movementTimestamp; public function SimpleMovement() { //step 1: create player object playerObject = new Sprite(); playerObject.graphics.lineStyle(1, 0x000000); playerObject.graphics.beginFill(0x6D7B8D); playerObject.graphics.drawRect(0, 0, 25, 50); //make it rotate around the center playerObject.x = 0 - playerObject.width / 2; playerObject.y = 0 - playerObject.height / 2; shipContainer = new Sprite(); shipContainer.addChild(playerObject); shipContainer.x = 100; shipContainer.y = 100; shipContainer.rotation = 180; addChild(shipContainer); //step 2: install keyboard hook when stage is ready addEventListener(Event.ADDED_TO_STAGE, stageReady, false, 0, true); //step 3: install rendering update poll addEventListener(Event.ENTER_FRAME, updatePoller, false, 0, true); } private function updatePoller(event:Event):void { var newTime:Number = getTimer(); //turning if (turningMode != 0) { var turningDeltaTime:Number = newTime - turningTimestamp; turningTimestamp = newTime; var rotation:Number = TURNING_SPEED * turningDeltaTime / 1000; if (turningMode == 1) shipContainer.rotation -= rotation; else shipContainer.rotation += rotation; } //movement if (moving) { var movementDeltaTime:Number = newTime - movementTimestamp; movementTimestamp = newTime; var distance:Number = MOVEMENT_SPEED * movementDeltaTime / 1000; var rAngle:Number = shipContainer.rotation * RADIAN_DIVIDE; //convert degrees to radian shipContainer.x += distance * Math.sin(rAngle); shipContainer.y -= distance * Math.cos(rAngle); } } private function stageReady(event:Event):void { //install keyboard hook stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDown, false, 0, true); stage.addEventListener(KeyboardEvent.KEY_UP, keyUp, false, 0, true); } private final function keyDown(event:KeyboardEvent):void { if ((event.keyCode == 87) && (!moving)) //87 = W { movementTimestamp = getTimer(); moving = true; } if ((event.keyCode == 65) && (turningMode != 1)) //65 = A { turningTimestamp = getTimer(); turningMode = 1; } else if ((event.keyCode == 68) && (turningMode != 2)) //68 = D { turningTimestamp = getTimer(); turningMode = 2; } } private final function keyUp(event:KeyboardEvent):void { if ((event.keyCode == 87) && (moving)) moving = false; //87 = W if (((event.keyCode == 65) || (event.keyCode == 68)) && (turningMode != 0)) turningMode = 0; //65 = A, 68 = D } } } The results were as I expected. Absolutely no improvement. I really hope that someone has another suggestion as this thing needs fixing. Also, I doubt it's my system as I have a pretty good one (8GB RAM, Q9550 QuadCore intel, ATI Radeon 4870 512MB). Also, everyone else I asked so far had the same issue with my client. Update 5: another example of a smooth flash game just to demonstrate that my movement definitely is different! See http://www.spel.nl/game/bumpercraft.html Update 4: I traced the time before rendering (EVENT.RENDER) and right after rendering (EVENT.ENTER_FRAME), the results: rendering took: 14 ms rendering took: 14 ms rendering took: 12 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 14 ms rendering took: 12 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 14 ms rendering took: 12 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 14 ms rendering took: 14 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 24 ms rendering took: 18 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 232 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms rendering took: 14 ms rendering took: 16 ms rendering took: 12 ms rendering took: 14 ms rendering took: 12 ms The range is 12-16 ms. During these differences, the shocking/warping/flickering movement was already going on. There is also 1 peak of 232ms, at this time there was a relatively big warp. This is however not the biggest problme, the biggest problem are the continuous small warps during normal movement. Does this give anyone a clue? Update 3: After testing, I know that the following factors are not causing my problem: Bitmap's quality - changed with photoshop to an uglier 8 colours optimized graphic, no improvement at all. Constant rotation of image while turning - disabled it, no improvement at all Browser rendering - tried to use the flash player standalone, no improvement at all I am 100% convinced that the problem lies in either my code or in my algorithm. Please, help me out. It has been almost two weeks (1 week that I asked this question on SO) now and I still have to get my golden answer. Update 1: see bottom for full flex project source and a live demo demonstrating my problem. I'm working on a 2d flash game. Player ships are created as an object: ships[id] = new GameShip(); When movement and rotation information is available, this is being directed to the corresponding ship: ships[id].setMovementMode(1); //move forward Now, within this GameShip object movement works using the "Event.ENTER_FRAME" event: addEventListener(Event.ENTER_FRAME, movementHandler); The following function is then being run: private final function movementHandler(event:Event):void { var newTimeStamp:uint = UtilLib.getTimeStamp(); //set current timeStamp var distance:Number = (newTimeStamp - movementTimeStamp) / 1000 * movementSpeed; //speed = x pixels forward every 1 second movementTimeStamp = newTimeStamp; //update old timeStamp var diagonalChange:Array = getDiagonalChange(movementAngle, distance); //the diagonal position update based on angle and distance charX += diagonalChange[0]; charY += diagonalChange[1]; if (shipContainer) { //when the container is ready to be worked with shipContainer.x = charX; shipContainer.y = charY; } } private final function getDiagonalChange(angle:Number, distance:Number):Array { var rAngle:Number = angle * Math.PI/180; //convert degrees to radian return [Math.sin(rAngle) * distance, (Math.cos(rAngle) * distance) * -1]; } When the object is no longer moving, the event listener will be removed. The same method is being used for rotation. Everything works almost perfect. I've set the project's target FPS to 100 and created a FPS counter. According to the FPS counter, the average FPS in firefox is around 100, while the top is 1000 and the bottom is 22. I think that the bottom and top FPSs are only happening during the initialization of the client (startup). The problem is that the ship appears to be almost perfectly smooth, while it should be just that without the "almost" part. It's almost as if the ship is "flickering" very very fast, you can't actually see it but it's hard to focus on the object while it's moving with your eyes. Also, every now and then, there seems to be a bit of a framerate spike, as if the client is skipping a couple of frames, you then see it quickly warp. It is very difficult to explain what the real problem is, but in general it's that the movement is not perfectly smooth. So, do you have any suggestions on how to make the movement or transition of objects perfectly smooth? Update 1: I re-created the client to demonstrate my problem. Please check it out. The client: http://feedpostal.com/test/MovementTest.html The Actionscript Project (full source): http://feedpostal.com/test/MovementTest.rar An example of a smooth flash game (not created by me): http://www.gamesforwork.com/games/swf/Mission%20Racing_august_10th_2009.swf It took me a pretty long time to recreate this client side version, I hope this will help with solving the problem. Please note: yes, it is actually pretty smooth. But it is definitely not smooth enough.

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• FileNet P8 workplace token issue in C#

  - by acadia

  Hello, I am trying to get user token and build the URL so that user need not login everytime they click the file. below is my code. My question is do I need to pass whole of the token value shown below or?? The token value I am getting is symmetric:algorithm:QUVT:keyid:NTZkYTNkNmI=:data:7P9aJHzkfGTOlwtotuWGaMqfU9COECscA9yxMdK64ZLa298A3tsGlHKHDFp0cH+gn/SiMrwKfbWNZybPXaltgo5e4H4Ak8KUiCRKWfS68qhmjfw69qPv9ib96vL3TzNORYFpp/hrwvp8aX4CQIZlBA== The problem is, once i copy the URL and past it in the browser, it is taking me to the login page. Though I am not getting any errors, it should take users directly to the imageviewer but instead it takes me to login page, if I login it is opening the file correctly. What am I doing wrong? string text = ""; string userName = "userName"; string pwd = "*****"; fileNetID = "{5FCE7E04-3D74-4A93-AA53-26C12A2FD4FC}"; Uri uri = null; string workplaceURL = "http://filenet:9081/WorkPlaceXT"; uri = new Uri(workplaceURL + "/setCredentials?op=getUserToken&userId=" + this.encodeLabel(userName) + "&password=" + this.encodeLabel(pwd) + "&verify=true"); System.Net.WebRequest webRequest = System.Net.WebRequest.Create(uri); System.Net.WebResponse webResponse = webRequest.GetResponse(); StreamReader streamReader = new StreamReader(webResponse.GetResponseStream()); String token = streamReader.ReadToEnd(); string contentURL = string.Empty; contentURL = workplaceURL + "/getContent?objectType=document&impersonate=true&objectStoreName=OBJECTSTORE&id=" + HttpUtility.UrlEncode(fileNetID); contentURL += "&ut=" + HttpUtility.UrlEncode(encodeLabel(token)); return contentURL;

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• OCR with Neural network: data extraction

  - by Sebastian Hoitz

  I'm using the AForge library framework and its neural network. At the moment when I train my network I create lots of images (one image per letter per font) at a big size (30 pt), cut out the actual letter, scale this down to a smaller size (10x10 px) and then save it to my harddisk. I can then go and read all those images, creating my double[] arrays with data. At the moment I do this on a pixel basis. So once I have successfully trained my network I test the network and let it run on a sample image with the alphabet at different sizes (uppercase and lowercase). But the result is not really promising. I trained the network so that RunEpoch had an error of about 1.5 (so almost no error), but there are still some letters left that do not get identified correctly in my test image. Now my question is: Is this caused because I have a faulty learning method (pixelbased vs. the suggested use of receptors in this article: http://www.codeproject.com/KB/cs/neural_network_ocr.aspx - are there other methods I can use to extract the data for the network?) or can this happen because my segmentation-algorithm to extract the letters from the image to look at is bad? Does anyone have ideas on how to improve it?

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• SHA512 vs. Blowfish and Bcrypt

  - by Chris

  I'm looking at hashing algorithms, but couldn't find an answer. Bcrypt uses Blowfish Blowfish is better than MD5 Q: but is Blowfish better than SHA512? Thanks.. Update: I want to clarify that I understand the difference between hashing and encryption. What prompted me to ask the question this way is this article, where the author refers to bcrypt as "adaptive hashing" http://chargen.matasano.com/chargen/2007/9/7/enough-with-the-rainbow-tables-what-you-need-to-know-about-s.html Since bcrypt is based on Blowfish, I was led to think that Blowfish is a hashing algorithm. If it's encryption as answers have pointed out, then seems to me like it shouldn't have a place in this article. What's worse is that he's concluding that bcrypt is the best. What's also confusing me now is that the phpass class (used for password hashing I believe) uses bcrypt (i.e. blowfish, i.e. encryption). Based on this new info you guys are telling me (blowfish is encryption), this class sounds wrong. Am I missing something?

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• java client program to send digest authentication request using HttpClient API

  - by Rajesh

  I have restlet sample client program which sends the digest request. Similar to this I need java client program which sends a digest request using HttpClient api. Can anybody send me sample code. Thanks in advance. Reference reference = new Reference("http://localhost:8092/authenticate"); Client client = new Client(Protocol.HTTP); Request request = new Request(Method.GET, reference); Response response = client.handle(request); System.out.println("response: "+response.getStatus()); Form form = new Form(); form.add("username", "rajesh"); form.add("uri", reference.getPath()); // Loop over the challengeRequest objects sent by the server. for (ChallengeRequest challengeRequest : response .getChallengeRequests()) { // Get the data from the server's response. if (ChallengeScheme.HTTP_DIGEST .equals(challengeRequest.getScheme())) { Series<Parameter> params = challengeRequest.getParameters(); form.add(params.getFirst("nonce")); form.add(params.getFirst("realm")); form.add(params.getFirst("domain")); form.add(params.getFirst("algorithm")); form.add(params.getFirst("qop")); } } // Compute the required data String a1 = Engine.getInstance().toMd5( "rajesh" + ":" + form.getFirstValue("realm") + ":" + "rajesh"); String a2 = Engine.getInstance().toMd5( request.getMethod() + ":" + form.getFirstValue("uri")); form.add("response", Engine.getInstance().toMd5( a1 + ":" + form.getFirstValue("nonce") + ":" + a2)); ChallengeResponse challengeResponse = new ChallengeResponse( ChallengeScheme.HTTP_DIGEST, "", ""); challengeResponse.setCredentialComponents(form); // Send the completed request request.setChallengeResponse(challengeResponse); response = client.handle(request); // Should be 200. System.out.println(response.getStatus());

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• How to correctly calculate FPS in XNA?

  - by Tomek Tarczynski

  I wrote a component to display current FPS. The most important part of it is: public override void Update(GameTime gameTime) { elapseTime += (float)gameTime.ElapsedRealTime.TotalSeconds; frameCounter++; if (elapseTime > 1) { FPS = frameCounter; frameCounter = 0; elapseTime = 0; } base.Update(gameTime); } In most cases it works ok, but recently I had a problem. When I put following code into Update method of game strange thing starts to happen. if (threadPath == null || threadPath.ThreadState != ThreadState.Running) { ThreadStart ts = new ThreadStart(current.PathFinder.FindPaths); threadPath = new Thread(ts); threadPath.Priority = ThreadPriority.Highest; threadPath.Start(); } Main idea of this code is to run pathFinding algorithm in different thread all the time. By strange things I mean that sometimes FPS drasticly decreases, this is obvious, but displayed FPS changes more often than once a second. If I understand this code FPS can't change more often than once a second. Can someone explain me what's going on?

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• Advice for last year college graduates

  - by Tomh

  Hey guys, I know there are many "advice" questions around this site. But I wanted to to narrow mine down to last year college students, in my case my last year as Master student in computer science. So far is a list of things I've done during my time in college (which I can recommend others to do aswell): Code a lot I've written several hobby projects, had part time jobs, entered the Imagine cup from Microsoft, took programming extensive courses and did freelance gigs. Read a lot I've bought most top books from the recommended book topics here, to be honest I have not read them all. learn different languages I've tried several languages including Haskell, Java, Python, Ruby, Lisp, Prolog, C#, PHP, JS, AS3 and possibly some more I forgot. Tried to start a blog Joel recommends to learn how to write, I tried starting a couple of blogs to improve upon this, I gave up on all instances after writing about three posts. It was just not my thing... Have a portfolio of launched projects/programs I'm busy with this, have a couple of finished, working projects I worked on to show to people. So this is my last year. Is there anything else you can recommend a last year college student to do before hitting the job market? Personally I'm tempted to spend my time on the following: Practice algorithm design Learn and memorize the usage of the low level API's of your favorite language Polish your portfolio Why? Because those first two will make sure you pass the majority of the interviews, here in Holland (I could be wrong). I rather not spend my time on those first two points, but I have to be realistic and thats just my experience on what kind of questions you'll get when you apply. The third point is my hope that I won't have to answer questions about the amount of standard types in c# for example if they can see I get projects done and launched. But I'm still graduating, so I don't know anything :), and many of you might be hiring grads on a recent base and could tell me and other interested people what you wish that the recent grads you interviewed would have done before they applied.

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• Development process for an embedded project with significant hardware changes

  - by pierr

  I have a good idea about Agile development process but it seems it does not fit well with a embedded project with significant hardware changes. I will describe below what we are currently doing (Ad-hoc way, no defined process yet). The changes are divided into three categories and different processes are used for each of them: complete hardware change example : use a different video codec IP a) Study the new IP b) RTL/FPGA simulation c) Implement the legacy interface - go to b) d) Wait until hardware (tape out) is ready f) Test on the real hardware hardware improvement example : enhance the image display quality by improving the underlying algorithm a) RTL/FPGA simulation b) Wait until hardware and test on the hardware Minor change example : only change hardware register mapping a) Wait until hardware and test on the hardware The worry is it seems we don't have too much control and confidence about software maturity for the hardware changes as the bring-up schedule is always very tight and the customer desired a seamless change when updating to a new version of hardware. How did you manage this kind of hardware change? Did you solve that by a Hardware Abstraction Layer (HAL)? Did you have a automatic test for the HAL layer? How did you test when the hardware platform is not even ready? Do you have well-documented processes for this kind of change?

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• Need help with artificial neural network

  - by deckard cain

  I have an input data for neural network that consists of 2 vectors with 200 elements, that i got from some program for generating signals. So it is actually 2x200 input to my nnet. As target data, i have one 1x200 vector that i also got from the same program. That is my training data set. I gather as much of those sets as i want so i transfer them to matlab and save them as, for example, set1, set2,.... When i am creating neural net, using newfit function (backropagation algorithm and everyhting else is set by default because i am kind of unexperianced with neural nets so i will have to experiment) i'm creating it using set1 only for example. Then, when i am to train neural net i train it for set1 then load set2 and train for it and so on. so its like this function net = create_fit_net(inputs,targets) numHiddenNeurons = 20; net = newfit(inputs,targets,numHiddenNeurons); net=train(net,inputs,targets); load set2; net=train(net,inputs,targets); load set3; net=train(net,inputs,targets); load set4; net=train(net,inputs,targets); i am using 4 sets of data here and all sets have variables of same name and size. My quesion is, am i doing this the right way, because, when doing simulation in some other m file, i am getting bad results, and every time i get different results. Does it matter if i create network with one set and then train with others too, and does it matter what set do i use to train network 1st? Also, i am confused about the amount of neurons to use (im using in the example 20 but actually i tried 1, 10, 30, 50, 100 200 and even 300 and i get nothing). If you have any suggestions, i'd be glad to take them into consideration. Any help is welcome. thanks in advance

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• Web crawler update strategy

  - by superb

  I want to crawl useful resource (like background picture .. ) from certain websites. It is not a hard job, especially with the help of some wonderful projects like scrapy. The problem here is I not only just want crawl this site ONE TIME. I also want to keep my crawl long running and crawl the updated resource. So I want to know is there any good strategy for a web crawler to get updated pages? Here's a coarse algorithm I've thought of. I divided the crawl process into rounds. Each round URL repository will give crawler a certain number (like , 10000) of URLs to crawl. And then next round. The detailed steps are: crawler add start URLs to URL repository crawler ask URL repository for at most N URL to crawl crawler fetch the URLs, and update certain information in URL repository, like the page content, the fetch time and whether the content has been changed. just go back to step 2 To further specify that, I still need to solve following question: How to decide the "refresh-ness" of a web page, which indicates the probability that this web page has been updated ? Since that is an open question, hopefully it will brought some fruitful discussion here.

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• Regarding: PKCS7, X509 and DER

  - by Sid

  Hi, I am novice to the "World of cryptography". I started working with OPENSSL. I need some information and basically I do have some doubts. I have a DER format file. I read the file using following command, "openssl x509 -inform DER -in filename.der -text" I got what I supposed to be. Following things I wanted to know: 1. What is the difference between PKCS7, DER and X509 ? (My understanding is, DER is format, X509 is certificate, and PKCS7 is the standard) I wrote a test file which accepts the DER file and outputs the version, serial number, Subject, Validity date before and Validity date after, But I am unable to get certificate verified. Following is the API Used. int i = X509_verify(X509 *x509 , X509_get_pubkey(X509 *x509)); But 'i' value is 'i' < 0(zero) This is why I am getting "Signature verification problems". How to overcome this? In My test file I am unable to read the "Signature Algorithm", "Subject Public Key Info", "X509v3 extensions" and "-----BEGIN CERTIFICATE-----" to "-----END CERTIFICATE-----" Please give some inputs. Thanks in Advance. openSid

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• Ruby on rails generates tests for you. Do those give a false sense of a safety net?

  - by Hamish Grubijan

  Disclaimer: I have not used RoR, and I have not generated tests. But, I will still dare to post this question. Quality Assurance is theoretically impossible to get 100% right in general (Undecidable problem ;), and it is hard in practice. So many developers do not understand that writing good automated tests is an art, and it is hard. When I hear that RoR generates the tests for you, I get very skeptical. It cannot be that easy. Testing is a general concept; it applies across languages. So does the concept of code contracts, it is similar for languages that support it. Code contracts do not generate themselves. The programmer must add the requirements and the promises manually, after doing some thinking about the algorithm / function. If a human gets it wrong, then the tools will propagate the error. Similarly with testing - it takes human judgement about what should happen. Tests do not write themselves, and we are far from the day when a business analyst can just have a conversation with a computer and tell it informally what the requirements are and have the computer do all the work. There is no magic ... how can RoR generate good tests for you? Please shed some light on this. Opinions are ok, for this is a community wiki. Thanks!

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• linebreak in url with Bibtex and hyperref package

  - by Tim

  Why is this item not shown properly in my bibliography? @misc{ann, abstract = {ANN is an implbmentation of nearest neighbor search.}, author = {David M. Mount and Sunil Arya}, howpublished = {\url{http://www.cs.umd.edu/~mount/ANN/}}, keywords = {knn}, posted-at = {2010-04-08 00:05:04}, priority = {2}, title = {ANN.}, url = "http://www.cs.umd.edu/~mount/ANN/", year = {2008} } @misc{Nilsson96introductionto, author = {Nilsson, Nils J.}, citeulike-article-id = {6995464}, howpublished = {\url{http://robotics.stanford.edu/people/nilsson/mlbook.html}}, keywords = {*file-import-10-04-11}, posted-at = {2010-04-11 06:52:28}, priority = {2}, title = {Introduction to Machine Learning: An Early Draft of a Proposed Textbook.}, year = {1996} } EDIT: I am using \usepackage{hyperref}, not \usepackage{url}. I don't know what changes I just made made the first item appear properly now @misc{ann, abstract = {ANN is an implbmentation of nearest neighbor search.}, author = {David M. Mount and Sunil Arya}, howpublished = {\url{http://www.cs.umd.edu/~mount/ANN/}}, keywords = {ann}, posted-at = {2010-04-08 00:05:04}, priority = {2}, title = {The \textsc{A}pproximate \textsc{N}earest \textsc{N}eighbor \textsc{S}earching \textsc{L}ibrary.}, url = "http://www.cs.umd.edu/~mount/ANN/", year = {2008} } EDIT: Since I am using hyperref package, it produces error when using url package together with it. So the two cannot work together? I would like to use hyper links inside pdf file, so I would like to use hyperref package instead of url package. I googled a bit, and try \usepackage[hyperindex,breaklinks]{hyperref}, but there is still no line break just as before. How can I do it? Is there conflict in the packages that I am now using?: \usepackage{amsmath} \usepackage{amsfonts} \usepackage[dvips]{graphicx} \usepackage{wrapfig} \graphicspath{{./figs/}} \DeclareGraphicsExtensions{.eps} \usepackage{fixltx2e} \usepackage{array} \usepackage{times} \usepackage{fancyhdr} \usepackage{multirow} \usepackage{algorithmic} \usepackage{algorithm} \usepackage{slashbox} \usepackage{multirow} \usepackage{rotating} \usepackage{longtable} \usepackage[hyperindex,breaklinks]{hyperref} \usepackage{forloop} \usepackage{lscape} \usepackage{supertabular} \usepackage{amssymb} \usepackage{amsthm}

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• SQL Server database with clustered GUID PKs - switch clustered index or switch to sequential (comb)

  - by Eyvind

  We have a database in which all the PKs are GUIDs, and most of the PKs are also the clustered index for the table. We know that this is bad (due to the random nature of GUIDs). So, it seems there are basically two options here (short of throwing out GUIDs as PKs altogether, which we cannot do (at least not at this time)). We could change the GUID generation algorithm to e.g. the one that NHibernate uses, as detailed in this post, or we could, for the tables that are under the heaviest use, change to a different clustered index, e.g. an IDENTITY column, and keep the "random" GUIDs as PKs. Is it possible to give any general recommendations in such a scenario? The application in question has 500+ tables, the largest one presently at about 1,5 million rows, a few tables around 500 000 rows, and the rest significantly lower (most of them well below 10K). Furthermore, the application is installed at several customer sites already, so we have to take any possible negative effects for existing customer into consideration. Thanks!

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• Text mining on large database (data mining)

  - by yox

  Hello, I have a large database of resumes (CV), and a certain table skills grouping all users skills. inside that table there's a field skill_text that describes the skill in full text. I'm looking for an algorithm/software/method to extract significant terms/phrases from that table in order to build a new table with standarized skills.. Here are some examples skills extracted from the DB : Sectoral and competitive analysis Business Development (incl. in international settings) Specific structure and road design software - Microstation, Macao, AutoCAD (basic knowledge) Creative work (Photoshop, In-Design, Illustrator) checking and reporting back on campaign progress organising and attending events and exhibitions Development : Aptana Studio, PHP, HTML, CSS, JavaScript, SQL, AJAX Discipline: One to one marketing, E-marketing (SEO & SEA, display, emailing, affiliate program) Mix marketing, Viral Marketing, Social network marketing. The output shoud be something like : Sectoral and competitive analysis Business Development Specific structure and road design software - Macao AutoCAD Photoshop In-Design Illustrator organising events Development Aptana Studio PHP HTML CSS JavaScript SQL AJAX Mix marketing Viral Marketing Social network marketing emailing SEO One to one marketing As you see only skills remains no other representation text. I know this is possible using text mining technics but how to do it ? the database is realy large.. it's a good thing because we can calculate text frequency and decide if it's a real skill or just meaningless text... The big problem is .. how to determin that "blablabla" is a skill ? thanks

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• I can't compile android projetc wiht JNI code

  - by lobi

  I'm trying to build simple android app with some JNI code. When I press build project in eclipse I get this error: Description Resource Path Location Type fatal error: algorithm: No such file or directory Tracker line 56, external location: /home/slani/code/OpenCV-2.4.6-android-sdk/sdk/native/jni/include/opencv2/core/core.hpp C/C++ Problem make: *** [obj/local/armeabi/objs/detect_jni/detect_jni.o] Error 1 Tracker C/C++ Problem Line 56 in core.hpp contains the relevant include. This is my Android.mk file jni folder: LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) include /home/slani/code/OpenCV-2.4.6-android-sdk/sdk/native/jni/OpenCV.mk LOCAL_MODULE := detect_jni LOCAL_SRC_FILES := detect_jni.cpp include $(BUILD_SHARED_LIBRARY) This is my Aplication.mk file in jni folder: APP_STL := gnustl_static APP_CPPFLAGS := -frtti -fexceptions APP_ABI := armeabi-v7a APP_PLATFORM := all This is my .cpp file: #include <jni.h> #include <opencv/cv.h> #include <opencv2/imgproc/imgproc.hpp> #include <opencv2/features2d/features2d.hpp> using namespace cv; extern "C"{ JNIEXPORT void JNICALL Java_com_slani_tracker_OpenCamera_findObject((JNIEnv *env, jlong addRgba, jlong addHsv); JNIEXPORT void JNICALL Java_com_slani_tracker_OpenCamera_findObject((JNIEnv *env, jlong addRgba, jlong addHsv) { Mat& rgba = *(Mat*)addRgba; Mat& hsv = *(Mat*)addHsv; cvtColor(rgba, hsv,CV_RGBA2HSV); } } Can someone please help me? What could be causing this problem? Thanks

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• Using Taylor Series to Avoid Loss of Precision

  - by Zachary

  I'm trying to use Taylor series to develop a numerically sound algorithm for solving a function. I've been at it for quite a while, but haven't had any luck yet. I'm not sure what I'm doing wrong. The function is f(x)=1 + x - sin(x)/ln(1+x) x~0 Also: why does loss of precision even occur in this function? when x is close to zero, sin(x)/ln(1+x) isn't even close to being the same number as x. I don't see where significance is even being lost. In order to solve this, I believe that I will need to use the Taylor expansions for sin(x) and ln(1+x), which are x - x^3/3! + x^5/5! - x^7/7! + ... and x - x^2/2 + x^3/3 - x^4/4 + ... respectfully. I have attempted to use like denominators to combine the x and sin(x)/ln(1+x) components, and even to combine all three, but nothing seems to work out correctly in the end. Any help is appreciated.

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• Lisp Style question label local functions or not?

  - by Andrew Myers

  I was wondering if there is a standard practice regarding the use of labels in Lisp. I've been messing around with a Lisp implementation of the algorithm described in the first answer here http://stackoverflow.com/questions/352203/generating-permutations-lazily My current version uses labels to break out portions of functionality. (defun next-permutation (pmute) (declare (vector pmute)) (let ((len (length pmute))) (if (> len 2) (labels ((get-pivot () (do ((pivot (1- len) (1- pivot))) ((or (= pivot 0) (< (aref pmute (1- pivot)) (aref pmute pivot))) pivot))) (get-swap (pivot) (let ((swp (1- len))) (loop for i from (1- len) downto pivot do (if (or (and (> (aref pmute i) (aref pmute (1- pivot))) (< (aref pmute i) (aref pmute swp))) (< (aref pmute swp) (aref pmute (1- pivot)))) (setf swp i))) swp)) (next (swp pivot) (rotatef (aref pmute (1- pivot)) (aref pmute swp)) (reverse-vector pmute pivot (1- len)))) (let ((piv (get-pivot))) (if (> piv 0) (next (get-swap piv) piv) nil)))))) Since each label is only called once I was wondering if this is considered bad practice since the only reason to do it in this case is for aesthetic reasons. I would argue that the current version with labels is clearer but that may go against common wisdom that I'm not aware of, being new to Lisp.

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