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  • Are there well-known examples of web products that were killed by slow service?

    - by Jeremy Wadhams
    It's a basic tenet of UX design that users prefer fast pages. http://www.useit.com/alertbox/response-times.html http://www.nytimes.com/2012/03/01/technology/impatient-web-users-flee-slow-loading-sites.html?pagewanted=all It's supposedly even baked into Google's ranking algorithm now: fast sites rank higher, all else being equal. But are there well known examples of web services where the popular narrative is "it was great, but it was so slow people took their money elsewhere"? I can pretty easily think of example problems with scale (Twitter's fail whale) or reliability (Netflix and Pinterest outages caused by a single datacenter in a storm). But can (lack of) speed really kill?

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • Assignment of roles in communication when sides could try to cheat

    - by 9000
    Assume two nodes in a peer-to-peer network initiating a communication. In this communication, one node has to serve as a "sender", another as a "receiver" (role names are arbitrary here). I'd like the nodes to assert either role with approximately equal probability. That is, in N communications with various other nodes a given node would assume the "sender" role roughly N/2 times. Since there's no third-party arbiter available, nodes should agree on their roles by exchanging messages. The catch is that we can encounter a rogue node which would try to become the "receiver" in most or all cases, and coax the other side to always serve as a "sender". I'm looking for an algorithm to assign roles to sides of communication so that no side could get a predetermined role with high probability. It's OK for the side which is trying to cheat to fail to communicate.

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  • Why does a proportional controller have a steady state error?

    - by Qantas 94 Heavy
    I've read about feedback loops, how much this steady state error is for a given gain and what to do to remove this steady state error (add integral and/or derivative gains to the controller), but I don't understand at all why this steady state error occurs in the first place. If I understand how a proportional control works correctly, the output is equal to the current output plus the error, multiplied by the proportional gain (Kp). However, wouldn't the error slowly diminish over time as it is added (reaching 0 at infinite time), not have a steady state error? From my confusion, it seems I'm completely misunderstanding how it works - a proper explanation of how this steady state error eventuates would be fantastic.

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  • Trying to figure out SDL pixel manipulation?

    - by NoobScratcher
    Hello so I've found code that plots a pixel in an SDL Screen Surface : void putpixels(int x, int y, int color) { unsigned int *ptr = (unsigned int*)Screen->pixels; int lineoffset = y * (Screen->pitch / 4 ); ptr[lineoffset + x ] = color; } But I have no idea what its actually doing here this is my thoughts. You make an unsigned integer to hold the unsigned int version of pixels then you make another integer to hold the line offset and it equals to multiply by pitch which is then divided by 4 ... Now why am I dividing it by 4 and what is the pitch and why do I multiply it?? Why must I change the lineoffset and add it to the x value then equal it to colors? I'm soo confused.. ;/ I found this function here - http://sol.gfxile.net/gp/ch02.html

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  • How do I morph between meshes that have different vertex counts?

    - by elijaheac
    I am using MeshMorpher from the Unify wiki in my Unity project, and I want to be able to transform between arbitrary meshes. This utility works best when there are an equal number of vertices between the two meshes. Is there some way to equalize the vertex count between a set of meshes? I don't mean that this would reduce the vertex count of a mesh, but would rather add redundant vertices to any meshes with smaller counts. However, if there is an alternate method of handling this (other than increasing vertices), I would like to know.

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  • Strategy/algorithm to divide fair teams based on history

    - by Vegar
    We are a group of people playing floorball together on a regular basis. Every session starts with the daunting task of dividing teams... So what would be better than an application to pick teams automatically? So, given a history of team-combinations and results, and a list of people showing up for this particular session, what would be a good strategy to find the optimal teams? By optimal, I mean teams as equal as possible. Any ideas? Edit: To make it clear, the date that I have to base the picking on, would be something like this: [{ team1: ["playerA", "playerB", "playerC"], team2: ["playerD", "playerE", "playerF"], goals_team1: 10, goals_team2: 8 }, { team1: ["playerD", "playerB", "playerC"], team2: ["playerA", "playerE", "playerG"], goals_team1: 2, goals_team2: 5 }, { team1: ["playerD", "playerB", "playerF"], team2: ["playerA", "playerE", "playerC"], goals_team1: 4, goals_team2: 2 }]

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  • What is the difference between these senior software engineer titles?

    - by stackoverflowuser2010
    I'm currently a senior research software engineer at a large company and am being offered a "senior staff engineer" position somewhere else. I am not sure if the new position's title conveys a sideways move or an advancement. So, all other things being roughly equal (salary, domain of expertise, etc.), what is the external difference between these software engineer titles (in general and regardless of any particular company, if possible): senior engineer senior research engineer senior staff engineer member of technical staff principal engineer Edit: Let me elaborate on "member of technical staff" since it's kind of uncommon. I think it's a high title, commonly associated with research. I know that Oracle, VMWare, and the old Bell Labs have these titles. See: Member of Technical Staff . I know what it means, but I don't know how it stacks up against the other titles, which is why I asked.

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  • DX10 sprite and pixel shader

    - by Alex Farber
    I am using ID3DX10Sprite to draw 2D image on the screen. 3D scene contains only one textured sprite placed over the whole window area. Render method looks like this: m_pDevice-ClearRenderTargetView(...); m_pSprite-Begin(D3DX10_SPRITE_SORT_TEXTURE); m_pSprite-DrawSpritesImmediate(&m_SpriteDefinition, 1, 0, 0); m_pSprite-End(); Now I want to make some transformations with the sprite texture in a shader. Currently the program doesn't work with shader. How it is possible to add pixel shader to the program with this structure? Inside the shader, I need to set all colors equal to red, and multiply pixel values by some coefficient. Something like this: float4 TexturePixelShader(PixelInputType input) : SV_Target { float4 textureColor; textureColor = shaderTexture.Sample(SampleType, input.tex); textureColor.x = textureColor.x * coefficient; textureColor.y = textureColor.x; textureColor.z = textureColor.x; return textureColor; }

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  • Does having a Google "stop word" in a domain name have less SEO benefit than not having it?

    - by Dan
    Let me explain. Let's say my keyword I want to optimize is "green giraffes". But the domain greengiraffes.com (singular, plural, no hyphen, hyphen, etc.) is not available. I know that the search results for "green giraffes" and "about green giraffes" are essentially the same because "about" is a "stop word". Does that therefore also mean that the domain name "aboutgreengiraffes.com" is as good as "greengiraffes.com" in terms of SEO value? Are all stop words equal in that regard, or a shorter one (such as "e" or "z") is better?

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  • Manually updating HTML5 local storage?

    - by hustlerinc
    I'm just starting out HTML5 game developement (and game dev in general) and watching all the videos and tutorials available something has crossed my mind. Everyone keep saying I should set the cookie's (or cached files) to be expired after a certain amount of time. So that when it reaches that time the browser automatically downloads all assets again, even if it's the same asset's. Wouldn't it be possible to manually define the version of the game? For example the user has downloaded all the files for 1.01 of the game, when updating I change a simple variable to 1.02. When the user logs in it would compare his version to the current and if they are not equal only then it downloads the files? This could even be improved to download only specific files depending on what needs to be updated? Would this be possible or am I just dreaming? What are the possible downsides of this approach?

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  • k-d tree implementation [closed]

    - by user466441
    when i run my code and debugged,i got this error - this 0x00093584 {_Myproxy=0x00000000 _Mynextiter=0x00000000 } std::_Iterator_base12 * const - _Myproxy 0x00000000 {_Mycont=??? _Myfirstiter=??? } std::_Container_proxy * _Mycont CXX0017: Error: symbol "" not found _Myfirstiter CXX0030: Error: expression cannot be evaluated + _Mynextiter 0x00000000 {_Myproxy=??? _Mynextiter=??? } std::_Iterator_base12 * but i dont know what does it means,code is this #include<iostream> #include<vector> #include<algorithm> using namespace std; struct point { float x,y; }; vector<point>pointleft(4); vector<point>pointright(4); //we are going to implement two comparison function for x and y coordinates,we need it in calculation of median (we should sort vector //by x or y according to depth informaton,is depth even or odd. bool sortby_X(point &a,point &b) { return a.x<b.x; } bool sortby_Y(point &a,point &b) { return a.y<b.y; } //so i am going to implement to median finding algorithm,one for finding median by x and another find median by y point medianx(vector<point>points) { point temp; sort(points.begin(),points.end(),sortby_X); temp=points[(points.size()/2)]; return temp; } point mediany(vector<point>points) { point temp; sort(points.begin(),points.end(),sortby_Y); temp=points[(points.size()/2)]; return temp; } //now construct basic tree structure struct Tree { float x,y; Tree(point a) { x=a.x; y=a.y; } Tree *left; Tree *right; }; Tree * build_kd( Tree *root,vector<point>points,int depth) { point temp; if(points.size()==1)// that point is as a leaf { if(root==NULL) root=new Tree(points[0]); return root; } if(depth%2==0) { temp=medianx(points); root=new Tree(temp); for(int i=0;i<points.size();i++) { if (points[i].x<temp.x) pointleft[i]=points[i]; else pointright[i]=points[i]; } } else { temp=mediany(points); root=new Tree(temp); for(int i=0;i<points.size();i++) { if(points[i].y<temp.y) pointleft[i]=points[i]; else pointright[i]=points[i]; } } return build_kd(root->left,pointleft,depth+1); return build_kd(root->right,pointright,depth+1); } void print(Tree *root) { while(root!=NULL) { cout<<root->x<<" " <<root->y; print(root->left); print(root->right); } } int main() { int depth=0; Tree *root=NULL; vector<point>points(4); float x,y; int n=4; for(int i=0;i<n;i++) { cin>>x>>y; points[i].x=x; points[i].y=y; } root=build_kd(root,points,depth); print(root); return 0; } i am trying ti implement in c++ this pseudo code tuple function build_kd_tree(int depth, set points): if points contains only one point: return that point as a leaf. if depth is even: Calculate the median x-value. Create a set of points (pointsLeft) that have x-values less than the median. Create a set of points (pointsRight) that have x-values greater than or equal to the median. else: Calculate the median y-value. Create a set of points (pointsLeft) that have y-values less than the median. Create a set of points (pointsRight) that have y-values greater than or equal to the median. treeLeft = build_kd_tree(depth + 1, pointsLeft) treeRight = build_kd_tree(depth + 1, pointsRight) return(median, treeLeft, treeRight) please help me what this error means?

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  • Drag camera/view in a 3D world

    - by Dono
    I'm trying to make a Draggable view in a 3D world. Currently, I've made it using mouse position on the screen, but, when I move the distance traveled by my mouse is not equal to the distance traveled in the 3D world. So, I've tried to do that : Compute a ray from mouse position to 3D world. Calculate intersection with the ground. Check intersection difference old position <- new position. Translate camera with the difference. I've got a problem with this method: The ray is computed with the current camera's position I move the camera I compute the new ray with new camera position. The difference between old ray and new ray is now invalid. So, graphically my camera don't stop to move to previous/new position everytime. How can I do a draggable camera with another solution ? Thanks!

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  • Working with different URL structures

    - by Dane411
    As I'm quite newbie to this field, I've doubts and there are some I couldn't find on Google, i.e: If I'm not wrong, index.html makes it possible to avoid to add the filename to the url, www.example.com/ is equal to www.example.com/index.html. And that works for the following subdirectories, right? www.example.com/music/ Is there any other way to achieve this without using an index.html file? (I've read smth about converting dynamic urls to static: ./?var1=value1&varN=valueN - ./value1/valueN) How can I convert www.example.com/music/ to music.example.com/ and why should it be used? Thanks in advance!

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  • What is the term that means "keeping the arguments for different API calls as similar as possible"?

    - by larson4
    There is a word which I can never remember... it expresses a design goal that API calls (or functions or methods or whatever) should be as similar as reasonably possible in their argument patterns. It may also extend to naming as well. In other words, all other things being equal, it is probably bad to have these three functions: deleteUser(email) petRemove(petId,species) destroyPlanet(planetName,starName) if instead you could have deleteUser(userId) deletePet(petId) deletePlanet(planetId) What is the word for this concept? I keep thinking it's "orthogonal" but it definitely isn't. Its a very important concept, and to me it's one of the biggest things that makes some APIs a joy to work with (because once you learn a few things you can pretty much use everything without looking at doco), and others a pain (because every function is done inconsistently).

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  • What does Visual studio debugger do, when condition should give error

    - by zacharmarz
    I'm debugging some code and I need to break everytime, when character in string (const char *) is equal to something. So I put there breakpoint and attach condition like: s[0] == 'e'. But code I'm debugging is in CRT and there is possibility, that s == 0 is true. So "addressing empty pointer" should give some kind of error. Yes - I could give there condition s != 0, but it would not be such fun :) And I'm curious, what will debugger do when trying to evaluate this condition? How it will behave internally? Obviously it's not giving any error nor stopping on this breakpoint when s == 0 Thanks for your answer.

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  • Lightweight Ubuntu

    - by Nick Berardi
    Just to start off, I know of lubuntu but it really doesn't meet what I am looking for. Basically what I am looking for is the standard Desktop Ubuntu install, but with out all the word processing, multimedia, and games installed. I have seen posts out about how to get the desktop environment running on Ubuntu server, but they seem complicated, and never seem to equal the standard Desktop install. So my question is, is there anyway to tell the standard Desktop install not to install all the applications? Or is there a distro available that leaves all the applications out, and just has the standard desktop look and feel? What I really want this for is, is for development purposes to run on a VM to do Mono development.

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  • rel="Canonical": Ranking Benefits ? & specifying for PDF?

    - by Miak
    I think I understand the basic case for using rel="canonical": to tell google which is the preferred URI when the same page/content may be accessed via more than one URI. This helps you avoid duplicate content penalties. But what else does it do? Does it also affect search ranking? i.e. will the page I specify in the canonical be ranked higher than the others? (if all else equal). And in the case of PDF documents, I understand that you can now specify rel="canonical" for them too, using HTTP headers (i.e. in htaccess). Again, this would obviously help avoid dupilcate content penalties if the PDF content is the same as the HTML page or if it can be accessed in more than one place. But does it affect ranking? or are there any other benefits to doing this.

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  • Brightness fn key adjustment problems

    - by npCoder
    My brightness function key controls work after setting grub boot parameter to "acpi_osi=" but using them I cannot adjust the brightness higher than around 70% (there is empty bar left over and I can't adjust higher) unless I go to Brightness & Lock settings manually than I can use the slider to adjust it higher... I primarily use intel_backlight to adjust my backlight and I am running Linux kernel 3.14.1 on Ubuntu 14.04 LTS on an ASUS X550LA Laptop when I try: cd /sys/class/backlight/intel_backlight cat max_brightness 937 cat brightness 811 It seems that I can only adjust to a maximum of 811 using the fn brightness controls If I instead do cd /sys/class/backlight/acpi_video0 cat max_brightness 10 cat brightness 4 cat actual_brightness 10 With the FN keys actual_brightness is not equal to the value returned from brightness on acip_video0 (which is always 4) but on intel_backlight actual_brightness = brightness The adjustment problem seemingly arises because both intel_backlight and acpi_video0 are trying to adjust brightness

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  • Permissions depending on parameters passed to application

    - by Engineiro
    I have a java app that writes to a very important table I have. This is sudo protected, but this app takes a parameters for where the output should go. The default is the REAL DEAL but the "output" parameter takes priority over the default, so if a user provides a path that they have write permission for, say: /home/username/mystuff then I would like for users to be allowed to write to these directories. The app is launched in a shell script, so I am wondering if I can check that the string does not equal /path/to/real/deal and not empty (since /path/to/real/deal is the default) and allow users to write to places they have permissions for. My impression of linux permissions is that it is tied to the application itself and cannot be conditionally approved, but I wonder if there is some bash fu or alternative method I can perform to get me my desired result. Using Ubuntu 10.04.4 LTS

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  • Compare a variable that can have numeric or string as value

    - by Tarun
    I have a variable named Seconds_Behind_Master from one of my scripts. The problem is that this variable can either have a numeric value or can also take a string NULL as its value. Now, when I try to execute this script in shell it gets executed but gives a warning like this: [: Illegal number: NULL I believe it is due to the fact that in this case the value is NULL but when it compares it with numeral value 60 it gives this warning. How can I rectify it? Here is the piece of code: Seconds_Behind_Master=$Show_Slave_Status | grep "Seconds_Behind_Master" | awk -F": " {' print $2 '} if [ "$Seconds_Behind_Master" -ge "60" ]; then echo "replication delayed greater than or equal to 60." else if [ "$Seconds_Behind_Master" = "NULL" ]; then echo "Delay is Null." fi fi

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  • How to divide hex grid evenly among n players?

    - by manabreak
    I'm making a simple hex-based game, and I want the map to be divided evenly among the players. The map is created randomly, and I want the players to have about equal amount of cells, with relatively small areas. For example, if there's four players and 80 cells in the map, each of the players would have about 20 cells (it doesn't have to be spot-on accurate). Also, each player should have no more than four adjacent cells. That is to say, when the map is generated, the biggest "chunks" cannot be more than four cells each. I know this is not always possible for two or three players (as this resembles the "coloring the map" problem), and I'm OK with doing other solutions for those (like creating maps that solve the problem instead). But, for four to eight players, how could I approach this problem? As always, any and all help is appreciated. :)

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  • Does it make a difference if I declare variables inside or outside a loop in Java?

    - by Puckl
    Does it make a difference if I declare variables inside or outside a loop in Java? Is this for(int i = 0; i < 1000; i++) { int temporaryValue = someMethod(); list.add(temporaryValue) } equal to this (with respect to memory usage)? int temporaryValue = 0; for(int i = 0; i < 1000; i++) { temporaryValue = someMethod(); list.add(temporaryValue) } And what if the temporary variable is for example an ArrayList? for(int i = 0; i < 1000; i++) { ArrayList<Integer> array = new ArrayList<Integer>(); fillArray(array); // do something with the array }

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  • Partitioning set into subsets with respect to equality of sum among subsets

    - by Al.Net
    let say i have {3, 1, 1, 2, 2, 1,5,2,7} set of numbers, I need to split the numbers such that sum of subset1 should be equal to sum of subset2 {3,2,7} {1,1,2,1,5,2}. First we should identify whether we can split number(one way might be dividable by 2 without any remainder) and if we can, we should write our algorithm two create s1 and s2 out of s. How to proceed with this approach? I read partition problem in wiki and even in some articles but i am not able to get anything. Can someone help me to find the right algorithm and its explanation in simple English?

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  • Circular movement - eliminating speed ups near Y = 0

    - by Fibericon
    I have a basic algorithm to rotate an enemy around a 200 unit radius circle with center 0. This is how I'm achieving that: if (position.Y <= 0 && position.X > -200) { position.X -= 2; position.Y = 0 - (float)Math.Sqrt((200 * 200) - (position.X * position.X)); } else { position.X += 2; position.Y = (float)Math.Sqrt((200 * 200) - (position.X * position.X)); } It does work, and I've ensured that at no point does either X or Y equal NaN. However, when Y approaches 0, it seems to go significantly faster. This surprises me, because the Y values are locked to the X, which is being incremented by a steady amount. What can I do to smooth the speed?

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