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• Stack usage with MMX intrinsics and Microsoft C++

  - by arik-funke

  I have an inline assembler loop that cumulatively adds elements from an int32 data array with MMX instructions. In particular, it uses the fact that the MMX registers can accommodate 16 int32s to calculate 16 different cumulative sums in parallel. I would now like to convert this piece of code to MMX intrinsics but I am afraid that I will suffer a performance penalty because one cannot explicitly intruct the compiler to use the 8 MMX registers to accomulate 16 independent sums. Can anybody comment on this and maybe propose a solution on how to convert the piece of code below to use intrinsics? == inline assembler (only part within the loop) == paddd mm0, [esi+edx+8*0] ; add first & second pair of int32 elements paddd mm1, [esi+edx+8*1] ; add third & fourth pair of int32 elements ... paddd mm2, [esi+edx+8*2] paddd mm3, [esi+edx+8*3] paddd mm4, [esi+edx+8*4] paddd mm5, [esi+edx+8*5] paddd mm6, [esi+edx+8*6] paddd mm7, [esi+edx+8*7] ; add 15th & 16th pair of int32 elements esi points to the beginning of the data array edx provides the offset in the data array for the current loop iteration the data array is arranged such that the elements for the 16 independent sums are interleaved.

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• Optimal two variable linear regression SQL statement (censoring outliers)

  - by Dave Jarvis

  Problem Am looking to apply the y = mx + b equation (where m is SLOPE, b is INTERCEPT) to a data set, which is retrieved as shown in the SQL code. The values from the (MySQL) query are: SLOPE = 0.0276653965651912 INTERCEPT = -57.2338357550468 SQL Code SELECT ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM (SELECT D.AMOUNT, Y.YEAR FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE -- For a specific city ... -- C.ID = 8590 AND -- Find all the stations within a 15 unit radius ... -- SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) <15 AND -- Gather all known years for that station ... -- S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND -- The data before 1900 is shaky; insufficient after 2009. -- Y.YEAR BETWEEN 1900 AND 2009 AND -- Filtered by all known months ... -- M.YEAR_REF_ID = Y.ID AND -- Whittled down by category ... -- M.CATEGORY_ID = '001' AND -- Into the valid daily climate data. -- M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ORDER BY Y.YEAR ) t Data The data is visualized here (with five outliers highlighted): Questions How do I return the y value against all rows without repeating the same query to collect and collate the data? That is, how do I "reuse" the list of t values? How would you change the query to eliminate outliers (at an 85% confidence interval)? The following results (to calculate the start and end points of the line) appear incorrect. Why are the results off by ~10 degrees (e.g., outliers skewing the data)? (1900 * 0.0276653965651912) + (-57.2338357550468) = -4.66958228 (2009 * 0.0276653965651912) + (-57.2338357550468) = -1.65405406 I would have expected the 1900 result to be around 10 (not -4.67) and the 2009 result to be around 11.50 (not -1.65). Thank you!

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• How to draw a circle in java with a radius and points around the edge

  - by windopal

  Hi, I'm really stuck on how to go about programming this. I need to draw a circle within a JFrame with a radius and points around the circumference. i can mathematically calculate how to find the coordinates of the point around the edge but i cant seem to be able to program the circle. I am currently using a Ellipse2D method but that doesn't seem to work and doesn't return a radius, as under my understanding, it doesn't draw the circle from the center rather from a starting coordinate using a height and width. My current code is on a separate frame but i need to add it to my existing frame. import java.awt.*; import javax.swing.*; import java.awt.geom.*; public class circle extends JFrame { public circle() { super("circle"); setSize(410, 435); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Panel sp = new Panel(); Container content = getContentPane(); content.add(sp); setContentPane(content); setVisible(true); } public static void main (String args[]){ circle sign = new circle(); } } class Panel extends JPanel { public void paintComponent(Graphics comp) { super.paintComponent(comp); Graphics2D comp2D = (Graphics2D) comp; comp2D.setColor(Color.red); Ellipse2D.Float sign1 = new Ellipse2D.Float(0F, 0F, 350F, 350F); comp2D.fill(sign1); } }

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• Finding unreachable sections of a 2D map

  - by dada

  I don't want you to solve this problem for me, i just want to ask for some ideas. This is the input below, and it represents a map. The 'x' represents land, and the dots - water. So with the 'x' you can represent 'islands' on the map. xxx.x...xxxxx xxxx....x...x ........x.x.x ..xxxxx.x...x ..x...x.xxx.x ..x.x.x...x.. ..x...x...xxx ...xxxxxx.... x............ As you can see, there are some islands which are closed, i.e. if some boat is inside its territory, it won't be able to get out, for ex: ..xxxxx. ..x...x. ..x.x.x. ..x...x. ..xxxxx. And there are some open islands which is possible to get out of them, ex: .xxxxx .x...x .x.x.x .xxx.x The problem is this: For a given NxM map like those above, calculate howm any of the islands are open, and how many are closed. I repeat: I don't want you to solve it, just need some sugestions, ideas for solving. thanks

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• dynamically created arrays

  - by DevAno1

  My task consists of two parts. First I have to create globbal char array of 100 elements, and insert some text to it using cin. Afterwards calculate amount of chars, and create dedicated array with the length of the inputted text. I was thinking about following solution : char[100]inputData; int main() { cin >> inputData >> endl; int length=0; for(int i=0; i<100; i++) { while(inputData[i] == "\0") { ++count; } } char c = new char[count]; Am I thinking good ? Second part of the task is to introduce in the first program dynamically created array of pointers to all inserted words. Adding a new word should print all the previous words and if there is no space for next words, size of the inputData array should be increased twice. And to be honest this is a bit too much for me. How I can create pointers to words specifically ? And how can I increase the size of global array without loosing its content ? With some temporary array ?

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• Drawing half of a Bezier path in Raphael

  - by Fibericon

  Let's say I have a cubic Bezier path as follows (formatted for use with the Raphael path function): M55 246S55 247 55 248 Just an example. This was taken from my drawing application, where I use the cursor to draw a line when the user holds the mouse button down, kind of like a pencil or marker. I'm using jquery's mousemove event to draw the line between two points every time the user moves the mouse. There is another (the reference point) that is taken before the line is drawn, so that the Bezier curve can be created. Here's my question: is it possible to make Raphael only draw half of a given path? I'm aware of the getSubpath() function, but if my understanding of Bezier curves is correct, it would be rather difficult to calculate the second argument. The problem with the animate function is that it creates double lines (that is, it creates the curved line that I want, and the boxy line around it which should not be shown, possibly because the mouse is being moved faster than the animation can handle). Of course, if my approach itself is flawed in some way (or my understanding of the possible solutions), I'd like to hear it. Any help would be appreciated.

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• C Programming Logic Error?

  - by mbpluvr64

  The following code compiles fine, but does not allow the user to choose whether or not the program is to run again. After giving the user the answer, the program automatically terminates. I placed the main code in a "do while" loop to have the ability to convert more than one time if I wanted too. I have tried to run the program in the command line (Mac and Ubuntu machines) and within XCode with the exact same results. Any assistance would be greatly appreciated. C Beginner P.S. Compiling on MacBookPro running Snow Leopard. #include <stdio.h> #include <stdlib.h> int main(void) { char anotherIteration = 'Y'; do { const float Centimeter = 2.54f; float inches = 0.0f; float result = 0.0f; // user prompt printf("\nEnter inches: "); scanf("%f", &inches); if (inches < 0) { printf("\nTry again. Enter a positive number.\n"); break; } else { // calculate result result = inches * Centimeter; } printf("%0.2f inches is %0.2f centimeters.\n", inches, result); // flush input fflush(stdin); // user prompt printf("\nWould you like to run the program again? (Y/N): "); scanf("%c", &anotherIteration); if ((anotherIteration != 'Y') || (anotherIteration != 'N')) { printf("\nEnter a Y or a N."); break; } } while(toupper(anotherIteration == 'Y')); printf("Program terminated.\n"); return 0; }

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• Long text input from user and PDF generation

  - by Petteri Hietavirta

  I have built a web application that can be seen as an overcomplicated application form. There are bunch of text areas with a given character limit. After the form submission various things happen and one of them is PDF generation. The text is queried from the DB and inserted in the PDF template created in iReports. This works fine but the major pain is overflowing text. The maximum number of characters is set based on 'average' text. But sometimes people prefer to write with CAPS or add plenty of linefeeds to format their text. These then cause user's text to overflow the space given in PDF. Unfortunately the PDF document must look like a real application form so I cannot allow unlimited space. What kind of approaches you have used to tackle this? Clean/restrict user input? Calculate the space requirement of the text based on font metrics? Provide preview of the PDF? (too bad users are not allowed to change their input after submission...)

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• iterate trough each selecter jquery

  - by Sam Vloeberghs

  Hi I'm having problems calculating stuff on my web app. Here is the scenario: I have a html markup like this: <table> <tr> <td><span class="sub_total">10</span></td> </tr> <tr> <td><span class="sub_total">10</span></td> </tr> <tr> <td><span class="sub_total">10</span></td> </tr> </table> <p><span id="total"></span></p> I would like to calculate the main total of all the sub totals: var total; $('.sub_total').each(function(){ total = total + parseInt($(this).text()); }); $('#total').text(total); But I can't get this to work. I get a NaN notification.. Plz help and advice Greeting

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• SQL Query: How to determine "Seen during N hour" if given two DateTime time stamps?

  - by efess

  Hello all. I'm writing a statistics application based off a SQLite database. There is a table which records when users Login and Logout (SessionStart, SessionEnd DateTimes). What i'm looking for is a query that can show what hours user have been logged in, in sort of a line graph way- so between the hours of 12:00 and 1:00AM there were 60 users logged in (at any point), between the hours of 1:00 and 2:00AM there were 54 users logged in, etc... And I want to be able to run a SUM of this, which is why I can't bring the records into .NET and iterate through them that way. I've come up with a rather primative approach, a subquery for each hour of the day, however this approach has proved to be slow and slow. I need to be able to calculate this for a couple hundred thousand records in a split second.. SELECT case when (strftime('%s',datetime(date(sessionstart), '+0 hours')) > strftime('%s',sessionstart) AND strftime('%s',datetime(date(sessionstart), '+0 hours')) < strftime('%s',sessionend)) OR (strftime('%s',datetime(date(sessionstart), '+1 hours')) > strftime('%s',sessionstart) AND strftime('%s',datetime(date(sessionstart), '+1 hours')) < strftime('%s',sessionend)) OR (strftime('%s',datetime(date(sessionstart), '+0 hours')) < strftime('%s',sessionstart) AND strftime('%s',datetime(date(sessionstart), '+1 hours')) > strftime('%s',sessionend)) then 1 else 0 end as hour_zero, ... hour_one, ... hour_two, ........ hour_twentythree FROM UserSession I'm wondering what better way to determine if two DateTimes have been seen durring a particular hour (best case scenario, how many times it has crossed an hour if it was logged in multiple days, but not necessary)? The only other idea I had is have a "hour" table specific to this, and just tally up the hours the user has been seen at runtime, but I feel like this is more of a hack than the previous SQL. Any help would be greatly appreciated!

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• Invalid method declaration, return type required

  - by Brett Steen

  I am getting an error at public Rectangle(double width, double height){ saying that it's an invalid method declaration, return type required. I'm not sure how to fix it. These are also my instructions for my assignment: Write a super class encapsulating a rectangle. A rectangle has two attributes representing the width and the height of the rectangle. It has methods returning the perimeter and the area of the rectangle. This class has a subclass, encapsulating a parallelepiped, or box. A parallelepiped has a rectangle as its base, and another attribute, its length. It has two methods that calculate and return its area and volume. `public class Rectangle1 { private double width; private double height; public Rectangle1(){ } public Rectangle(double width, double height){ this.width = width; this.height = height; } public double getWidth(){ return width; } public void setWidth(double width) { this.width = width; } public double getHeight(){ return height; } public void setHeight(double height){ this.height = height; } public double getArea(){ return width * height; } public double getPerimeter(){ return 2 * (width + height); } } public class TestRectangle { public static void main(String[] args) { Rectangle1 rectangle = new Rectangle1(2,4); System.out.println("\nA rectangle " + rectangle.toString()); System.out.println("The area is " + rectangle.getArea()); System.out.println("The perimeter is " + rectangle.getPerimeter()); } }`

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• reddit style voting with django

  - by dotty

  Hay i need to hand implemeneting a voting system into a model. I've had a huge helping hand from Mike DeSimone making this work in the first place, but i need to expand upon his work. Here is my current code View def show_game(request): game = Game.objects.get(pk=1) discussions = game.gamediscussion_set.filter(reply_to=None) d = { 'game':game, 'discussions':discussions } return render_to_response('show_game', d) Template <ul> {% for discussion in discussions %} {{ discussion.html }} {% endfor %} </ul> Model class GameDiscussion(models.Model): game = models.ForeignKey(Game) message = models.TextField() reply_to = models.ForeignKey('self', related_name='replies', null=True, blank=True) created_on = models.DateTimeField(blank=True, auto_now_add=True) userUpVotes = models.ManyToManyField(User, blank=True, related_name='threadUpVotes') userDownVotes = models.ManyToManyField(User, blank=True, related_name='threadDownVotes') def html(self): DiscussionTemplate = loader.get_template("inclusions/discussionTemplate") return DiscussionTemplate.render(Context({ 'discussion': self, 'replies': [reply.html() for reply in self.replies.all()] })) DiscussionTemplate <li> {{ discussion.message }} {% if replies %} <ul> {% for reply in replies %} {{ reply }} {% endfor %} </ul> {% endif %} </li> As you can see we have 2 fields userUpVotes and userDownVotes on the model, these will calculate how to order the discussions and replies. How would i implement these 2 fields to order the replies and discussions based on votes? Any help would be great!

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• error C2512 in precompiled header file?

  - by SoloMael

  I'm having a ridiculously strange problem. When I try to run the program below, there's an error message that says: "error C2512: 'Record' : no appropriate default constructor available". And when I double-click it, it directs me to a precompiled read-only header file named "xmemory0". Do they expect me to change a read-only file? Here's the segment of code in the file it directs me to: void construct(_Ty *_Ptr) { // default construct object at _Ptr ::new ((void *)_Ptr) _Ty(); // directs me to this line } Here's the program: #include <iostream> #include <vector> #include <string> using namespace std; const int NG = 4; // number of scores struct Record { string name; // student name int scores[NG]; double average; // Calculate the average // when the scores are known Record(int s[], double a) { double sum = 0; for(int count = 0; count != NG; count++) { scores[count] = s[count]; sum += scores[count]; } average = a; average = sum / NG; } }; int main() { // Names of the class string names[] = {"Amy Adams", "Bob Barr", "Carla Carr", "Dan Dobbs", "Elena Evans"}; // exam scores according to each student int exams[][NG]= { {98, 87, 93, 88}, {78, 86, 82, 91}, {66, 71, 85, 94}, {72, 63, 77, 69}, {91, 83, 76, 60}}; vector<Record> records(5); return 0; }

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• PHP / C++ space calculations for parcel packing

  - by Andrew Willis

  I am working on a shopping cart project which requires a 'postage calculator' based on items that the person has in their cart. Obviously I will be storing the item's dimensions incl. weight and padding in a database and will also store the parcel (box) size and weight that the items will go in to, incl. box padding. Figuring the weight of the parcels will be easy but I was wondering how to go about figuring how to pack the box via PHP, that is, I would like the code to 'play tetris' with the items to make sure they get the best possible fit, giving accurate postage costs. Does anybody have any ideas on how best to achieve this or does anybody know of a PHP Class or function that can do this? EDIT: When I said 'best possible fit' maybe I was being optimistic! Having the script try every possible combination of package distribution within the parcel would be over the top, however I could improve the speed by writing the algoritm in C++ and running the program in PHP when the user 'checks out', the return value being an array with the parcel size and weight (which are all that are needed to calculate postage costs)

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• Reducing moire when downsampling halftone comic images.

  - by drawnonward

  How can I reduce moire effects when downsampling halftone comic book images during live zoom on an iPhone or iPad? I am writing a comic book viewer. It would be nice to provide higher resolution images and allow the user to zoom in while reading the comic book. However, my client is averse to moire effects and will not allow this feature if there are noticeable moire artifacts while zooming, which of course there are. Modifying the images to be less susceptible to moire would only work if the modifications were not perceptible. Blur was specifically prohibited, as is anything that removes the beloved halftone dots. The images are black and white halftone and line art. The originals are 600 dpi but what we ship with the application will be half that at best, so probably 2500 pixels or less tall. So what are my options? If I write a custom downsampling algorithm would it be fast enough for real time on these devices? Are there other tricks I can do? Would it work to just avoid the size ratios that have the most visual moire effects? As you zoom in an out, there are definitely peaks where the moire effects are worst. Is there a way to calculate what those points are and just zoom to a nearby scale that is not as bad? Any suggestions are welcome. I have very little experience with image and signal processing, but am enjoying the opportunity to learn. I know nothing of wavelets and acutance and other jargon, so please be verbose.

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• Mysql - What's wrong with the query...?

  - by SpikETidE

  Hi everybody.... I am trying to query a database to find the following If a customer searches for a hotel in a city between dates A and B, find and return the hotels in which rooms are free between the two dates. There will be more than one room in each room type(i.e. 5 Rooms in type A, 10 rooms in Type B etc) and we have to query the db to find only those hotels in which there is atleast one room free in atleast one type. This is my table structure.... **Structure for table 'reservations'** reservation_id hotel_id room_id customer_id payment_id no_of_rooms check_in_date check_out_date reservation_date **Structure for table 'hotels'** hotel_id hotel_name hotel_description hotel_address hotel_location hotel_country hotel_city hotel_type hotel_stars hotel_image hotel_deleted **Structure for table 'rooms'** room_id hotel_id room_name max_persons total_rooms room_price room_image agent_commision room_facilities service_tax vat city_tax room_description room_deleted And this is my query $city_search = '15'; $check_in_date = '29-03-2010'; $check_out_date = '31-03-2010'; $dateFormat_check_in = "DATE_FORMAT('$reservations.check_in_date','%d-%m-%Y')"; $dateFormat_check_out = "DATE_FORMAT('$reservations.check_out_date','%d-%m-%Y')"; $dateCheck = "$dateFormat_check_in >= '$check_in_date' AND $dateFormat_check_out <= '$check_out_date'"; $query = "SELECT $rooms.room_id, $rooms.room_name, $rooms.max_persons, $rooms.room_price, $hotels.hotel_id, $hotels.hotel_name, $hotels.hotel_stars, $hotels.hotel_type FROM $hotels,$rooms,$reservations WHERE $hotels.hotel_city = '$city_search' AND $hotels.hotel_id = $rooms.hotel_id AND $hotels.hotel_deleted = '0' AND $rooms.room_deleted = '0' AND $rooms.total_rooms - (SELECT SUM($reservations.no_of_rooms) as tot FROM $reservations WHERE $dateCheck GROUP BY $reservations.room_id) > '0'"; The number of rooms already reserved in each room type in each hotel will be stored in the reservations table... The thing is the query doesn't return any result at all...even though it should if i calculate it myself manually... I tried running the sub-query alone and i don't get any result... And i have lost quite some amount of hair trying to de-bug this query from yesterday... What's wrong with this...? Or is there a better way to do what i mentioned above...? Thanks for your time... Edit : Code edited to remove an bud... thanks to

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• How to import a class from default package

  - by mykhaylo

  Hi, I am using Eclipse 3.5 and I have created a project with some package structure along with the default package. I have one class in default package - Calculations.java and I want to make the use of that class in any of the package (for instance in com.company.calc). When I try to make the use of the class which is default package, its giving me compile error. Its not able to recognise the class in default package. Where is a problem? Calculations.java - source code public class Calculations{ native public int Calculate(int contextId); native public double GetProgress(int contextId); static { System.loadLibrary("Calc"); } } I can put my class in any other package. This class has some native method which is implemented in Delphi . If I put that class in any of the folder,I will have to make the change that DLL which I want to avoid(really - I can not). Thats why I put my class in the default package.

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• Problem with Restlet on GAE

  - by Leaf

  I'm trying to implement a calculator web service on GAE using Java Restlets... it works perfectly fine on localhost but when I upload my project to the Google App Engine everytime I try the web service link it says the link is broken. Here's the code I used: public Restlet createInboundRoot() { // Create a router Restlet that routes each call to a // new instance of HelloWorldResource. Router router = new Router(getContext()); Restlet restlet = new Restlet() { public void handle(Request request, Response response) { // Print the requested URI path String parameters = request.getResourceRef().getRemainingPart(); String message; if(parameters.charAt(0)=='?'){ message = "" + Calculator.calculate(parameters.substring(1)); } else { message = ""; } response.setEntity(message, MediaType.TEXT_PLAIN); } }; // Defines only one route router.attachDefault(restlet); return router; } The Application it's on is mapped to the /calcservice but as I said when I upload to GAE it comes back with a broken link error. I'm developing on Eclipse 3.4 and I'm wondering if there are any parameters I have to change to include the Restlet classes.

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• Calculating confidence intervals for a non-normal distribution

  - by Josiah

  Hi all, First, I should specify that my knowledge of statistics is fairly limited, so please forgive me if my question seems trivial or perhaps doesn't even make sense. I have data that doesn't appear to be normally distributed. Typically, when I plot confidence intervals, I would use the mean +- 2 standard deviations, but I don't think that is acceptible for a non-uniform distribution. My sample size is currently set to 1000 samples, which would seem like enough to determine if it was a normal distribution or not. I use Matlab for all my processing, so are there any functions in Matlab that would make it easy to calculate the confidence intervals (say 95%)? I know there are the 'quantile' and 'prctile' functions, but I'm not sure if that's what I need to use. The function 'mle' also returns confidence intervals for normally distributed data, although you can also supply your own pdf. Could I use ksdensity to create a pdf for my data, then feed that pdf into the mle function to give me confidence intervals? Also, how would I go about determining if my data is normally distributed. I mean I can currently tell just by looking at the histogram or pdf from ksdensity, but is there a way to quantitatively measure it? Thanks!

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• Automatic tracking algorithm

  - by nico

  Hi everyone, I'm trying to write a simple tracking routine to track some points on a movie. Essentially I have a series of 100-frames-long movies, showing some bright spots on dark background. I have ~100-150 spots per frame, and they move over the course of the movie. I would like to track them, so I'm looking for some efficient (but possibly not overkilling to implement) routine to do that. A few more infos: the spots are a few (es. 5x5) pixels in size the movement are not big. A spot generally does not move more than 5-10 pixels from its original position. The movements are generally smooth. the "shape" of these spots is generally fixed, they don't grow or shrink BUT they become less bright as the movie progresses. the spots don't move in a particular direction. They can move right and then left and then right again the user will select a region around each spot and then this region will be tracked, so I do not need to automatically find the points. As the videos are b/w, I though I should rely on brigthness. For instance I thought I could move around the region and calculate the correlation of the region's area in the previous frame with that in the various positions in the next frame. I understand that this is a quite naïve solution, but do you think it may work? Does anyone know specific algorithms that do this? It doesn't need to be superfast, as long as it is accurate I'm happy. Thank you nico

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• Optimization in Python - do's, don'ts and rules of thumb.

  - by JV

  Well I was reading this post and then I came across a code which was: jokes=range(1000000) domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)] I thought wouldn't it be better to calculate the value of len(jokes) once outside the list comprehension? Well I tried it and timed three codes jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)]' 10000000 loops, best of 3: 0.0352 usec per loop jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);l=len(jokes);domain=[(0,(l*2)-i-1) for i in range(0,l*2)]' 10000000 loops, best of 3: 0.0343 usec per loop jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);l=len(jokes)*2;domain=[(0,l-i-1) for i in range(0,l)]' 10000000 loops, best of 3: 0.0333 usec per loop Observing the marginal difference 2.55% between the first and the second made me think - is the first list comprehension domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)] optimized internally by python? or is 2.55% a big enough optimization (given that the len(jokes)=1000000)? If this is - What are the other implicit/internal optimizations in Python ? What are the developer's rules of thumb for optimization in Python? Edit1: Since most of the answers are "don't optimize, do it later if its slow" and I got some tips and links from Triptych and Ali A for the do's. I will change the question a bit and request for don'ts. Can we have some experiences from people who faced the 'slowness', what was the problem and how it was corrected? Edit2: For those who haven't here is an interesting read Edit3: Incorrect usage of timeit in question please see dF's answer for correct usage and hence timings for the three codes.

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• How to handle dates that repeat indefinitely

  - by Addsy

  I am implementing a fairly simple calendar on a website using PHP and MySQL. I want to be able to handle dates that repeat indefinitely and am not sure of the best way to do it. For a time limited repeating event it seems to make sense to just add each event within the timeframe into my db table and group them with some form of recursion id. But when there is no limit to how often the event repeats, is it better to a) put records in the db for a specific time frame (eg the next 2 years) and then periodically check and add new records as time goes by - The problem with this is that if someone is looking 3 years ahead, the event won't show up b) not actually have records for each event but instead when i check in my php code for events within a specified time period, calculate wether a repeated event will occur within this time period - The problem with this is that it means there isn't a specific record for each event which i can see being a pain when i then want to associate other info (attendance etc) with that event. It also seems like it might be a bit slow Has anyone tried either of these methods? If so how did it work out? Or is there some other ingenious crafty method i'm missing?

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• Handling missing/incomplete data in R--is there function to mask but not remove NAs?

  - by doug

  As you would expect from a DSL aimed at data analysis, R handles missing/incomplete data very well, for instance: Many R functions have an 'na.rm' flag that you can set to 'T' to remove the NAs: mean( c(5,6,12,87,9,NA,43,67), na.rm=T) But if you want to deal with NAs before the function call, you need to do something like this: to remove each 'NA' from a vector: vx = vx[!is.na(a)] to remove each 'NA' from a vector and replace it w/ a '0': ifelse(is.na(vx), 0, vx) to remove entire each row that contains 'NA' from a data frame: dfx = dfx[complete.cases(dfx),] All of these functions permanently remove 'NA' or rows with an 'NA' in them. Sometimes this isn't quite what you want though--making an 'NA'-excised copy of the data frame might be necessary for the next step in the workflow but in subsequent steps you often want those rows back (e.g., to calculate a column-wise statistic for a column that has missing rows caused by a prior call to 'complete cases' yet that column has no 'NA' values in it). to be as clear as possible about what i'm looking for: python/numpy has a class, 'masked array', with a 'mask' method, which lets you conceal--but not remove--NAs during a function call. Is there an analogous function in R?

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• UI Design, incase of numerous situations

  - by The King

  Hi... I'm creating a web form, where in there are around 12-15 Input Fields... You can have a look at the screen and The request is such that depending on the data the user selects in the Gridview and the DropDown list, the appropriate Textboxes and CheckBoxes needs to be displayed. Some times the conditions are very direct, like when the DDL value is "ABC", get only paid amount from the user. Sometime they are so complex like... IF DDL is "DEF" and Selected GPMS value is between 1000-2000, calculate the values of allowed, paid etc (using some formula) and the focus should be directed to Page No Field, leaving the other fields open incase user wants to edit... There are around 10-15 conditions like this. As this was done through agile, conditions were being added as and when, and wherever it feels appropriate (DDL on change Event, GridView on selecting change event etc... etc..) After completion, now I see the code has become a big chuck, is growing unmanageably... Now, I'm planning to clear this... From you experience, what you think is the best way to handle this. There is a possibility to add more conditions like this in future... Please let me know, incase you need more information. I'm currently developing this app in C# .Net WindowsForms Edit: Currently there are only three items (The Datagrid, the DDL, the OverrideAmt CheckBox) that change the way other fields behave... Almost all of the conditions will fall between the two situations I mentioned... Mostly they belong to "Enabling/Disabling".. "Setting of Values"... and "Changing Focus" or any combination of these.

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• Optimal two variable linear regression SQL statement

  - by Dave Jarvis

  Problem Am looking to apply the y = mx + b equation (where m is SLOPE, b is INTERCEPT) to a data set, which is retrieved as shown in the SQL code. The values from the (MySQL) query are: SLOPE = 0.0276653965651912 INTERCEPT = -57.2338357550468 SQL Code SELECT ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM (SELECT D.AMOUNT, Y.YEAR FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE -- For a specific city ... -- C.ID = 8590 AND -- Find all the stations within a 5 unit radius ... -- SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) <15 AND -- Gather all known years for that station ... -- S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND -- The data before 1900 is shaky; and insufficient after 2009. -- Y.YEAR BETWEEN 1900 AND 2009 AND -- Filtered by all known months ... -- M.YEAR_REF_ID = Y.ID AND -- Whittled down by category ... -- M.CATEGORY_ID = '001' AND -- Into the valid daily climate data. -- M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ORDER BY Y.YEAR ) t Data The data is visualized here: Questions How do I return the y value against all rows without repeating the same query to collect and collate the data? That is, how do I "reuse" the list of t values? How would you change the query to eliminate outliers (at an 85% confidence interval)? The following results (to calculate the start and end points of the line) appear incorrect. Why are the results off by ~10 degrees (e.g., outliers skewing the data)? (1900 * 0.0276653965651912) + (-57.2338357550468) = -4.66958228 (2009 * 0.0276653965651912) + (-57.2338357550468) = -1.65405406 I would have expected the 1900 result to be around 10 (not -4.67) and the 2009 result to be around 11.50 (not -1.65). Thank you!

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