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• Multithreading 2D gravity calculations

  - by Postman

  I'm building a space exploration game and I've currently started working on gravity ( In C# with XNA). The gravity still needs tweaking, but before I can do that, I need to address some performance issues with my physics calculations. This is using 100 objects, normally rendering 1000 of them with no physics calculations gets well over 300 FPS (which is my FPS cap), but any more than 10 or so objects brings the game (and the single thread it runs on) to its knees when doing physics calculations. I checked my thread usage and the first thread was killing itself from all the work, so I figured I just needed to do the physics calculation on another thread. However when I try to run the Gravity.cs class's Update method on another thread, even if Gravity's Update method has nothing in it, the game is still down to 2 FPS. Gravity.cs public void Update() { foreach (KeyValuePair<string, Entity> e in entityEngine.Entities) { Vector2 Force = new Vector2(); foreach (KeyValuePair<string, Entity> e2 in entityEngine.Entities) { if (e2.Key != e.Key) { float distance = Vector2.Distance(entityEngine.Entities[e.Key].Position, entityEngine.Entities[e2.Key].Position); if (distance > (entityEngine.Entities[e.Key].Texture.Width / 2 + entityEngine.Entities[e2.Key].Texture.Width / 2)) { double angle = Math.Atan2(entityEngine.Entities[e2.Key].Position.Y - entityEngine.Entities[e.Key].Position.Y, entityEngine.Entities[e2.Key].Position.X - entityEngine.Entities[e.Key].Position.X); float mult = 0.1f * (entityEngine.Entities[e.Key].Mass * entityEngine.Entities[e2.Key].Mass) / distance * distance; Vector2 VecForce = new Vector2((float)Math.Cos(angle), (float)Math.Sin(angle)); VecForce.Normalize(); Force = Vector2.Add(Force, VecForce * mult); } } } entityEngine.Entities[e.Key].Position += Force; } } Yeah, I know. It's a nested foreach loop, but I don't know how else to do the gravity calculation, and this seems to work, it's just so intensive that it needs its own thread. (Even if someone knows a super efficient way to do these calculations, I'd still like to know how I COULD do it on multiple threads instead) EntityEngine.cs (manages an instance of Gravity.cs) public class EntityEngine { public Dictionary<string, Entity> Entities = new Dictionary<string, Entity>(); public Gravity gravity; private Thread T; public EntityEngine() { gravity = new Gravity(this); } public void Update() { foreach (KeyValuePair<string, Entity> e in Entities) { Entities[e.Key].Update(); } T = new Thread(new ThreadStart(gravity.Update)); T.IsBackground = true; T.Start(); } } EntityEngine is created in Game1.cs, and its Update() method is called within Game1.cs. I need my physics calculation in Gravity.cs to run every time the game updates, in a separate thread so that the calculation doesn't slow the game down to horribly low (0-2) FPS. How would I go about making this threading work? (any suggestions for an improved Planetary Gravity system are welcome if anyone has them) I'm also not looking for a lesson in why I shouldn't use threading or the dangers of using it incorrectly, I'm looking for a straight answer on how to do it. I've already spent an hour googling this very question with little results that I understood or were helpful. I don't mean to come off rude, but it always seems hard as a programming noob to get a straight meaningful answer, I usually rather get an answer so complex I'd easily be able to solve my issue if I understood it, or someone saying why I shouldn't do what I want to do and offering no alternatives (that are helpful). Thank you for the help!

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• Stupid Geek Tricks: How to Perform Date Calculations in Windows Calculator

  - by Usman

  Would you like to know how many days old are you today? Can you tell what will be the date 78 days from now? How many days are left till Christmas? How many days have passed since your last birthday? All these questions have their answers hidden within Windows! Curious? Keep reading to see how you can answer these questions in an instant using Windows’ built-in utility called ‘Calculator’. No, no. This isn’t a guide to show you how to perform basic calculations on calculator. This is an application of a unique feature in the Calculator application in Windows, and the feature is called Date Calculation. Most of us don’t really use the Windows’ Calculator that much, and when we do, it’s only for an instant (to do small calculations). However, it is packed with some really interesting features, so lets go ahead and see how Date Calculation works. To start, open Calculator by pressing the winkey, and type calcul… (it should’ve popped up by now, if not, you can type the rest of the ‘…ator’ as well just to be sure). Open it. And by the way, this date calculation function works in both Windows 7 and 8. Why Does 64-Bit Windows Need a Separate “Program Files (x86)” Folder? Why Your Android Phone Isn’t Getting Operating System Updates and What You Can Do About It How To Delete, Move, or Rename Locked Files in Windows

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• SQL Spatial: Getting “nearest” calculations working properly

  - by Rob Farley

  If you’ve ever done spatial work with SQL Server, I hope you’ve come across the ‘nearest’ problem. You have five thousand stores around the world, and you want to identify the one that’s closest to a particular place. Maybe you want the store closest to the LobsterPot office in Adelaide, at -34.925806, 138.605073. Or our new US office, at 42.524929, -87.858244. Or maybe both! You know how to do this. You don’t want to use an aggregate MIN or MAX, because you want the whole row, telling you which store it is. You want to use TOP, and if you want to find the closest store for multiple locations, you use APPLY. Let’s do this (but I’m going to use addresses in AdventureWorks2012, as I don’t have a list of stores). Oh, and before I do, let’s make sure we have a spatial index in place. I’m going to use the default options. CREATE SPATIAL INDEX spin_Address ON Person.Address(SpatialLocation); And my actual query: WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT l.Name, a.AddressLine1, a.City, s.Name AS [State], c.Name AS Country FROM MyLocations AS l CROSS APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a JOIN Person.StateProvince AS s     ON s.StateProvinceID = a.StateProvinceID JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; Great! This is definitely working. I know both those City locations, even if the AddressLine1s don’t quite ring a bell. I’m sure I’ll be able to find them next time I’m in the area. But of course what I’m concerned about from a querying perspective is what’s happened behind the scenes – the execution plan. This isn’t pretty. It’s not using my index. It’s sucking every row out of the Address table TWICE (which sucks), and then it’s sorting them by the distance to find the smallest one. It’s not pretty, and it takes a while. Mind you, I do like the fact that it saw an indexed view it could use for the State and Country details – that’s pretty neat. But yeah – users of my nifty website aren’t going to like how long that query takes. The frustrating thing is that I know that I can use the index to find locations that are within a particular distance of my locations quite easily, and Microsoft recommends this for solving the ‘nearest’ problem, as described at http://msdn.microsoft.com/en-au/library/ff929109.aspx. Now, in the first example on this page, it says that the query there will use the spatial index. But when I run it on my machine, it does nothing of the sort. I’m not particularly impressed. But what we see here is that parallelism has kicked in. In my scenario, it’s split the data up into 4 threads, but it’s still slow, and not using my index. It’s disappointing. But I can persuade it with hints! If I tell it to FORCESEEK, or use my index, or even turn off the parallelism with MAXDOP 1, then I get the index being used, and it’s a thing of beauty! Part of the plan is here: It’s massive, and it’s ugly, and it uses a TVF… but it’s quick. The way it works is to hook into the GeodeticTessellation function, which is essentially finds where the point is, and works out through the spatial index cells that surround it. This then provides a framework to be able to see into the spatial index for the items we want. You can read more about it at http://msdn.microsoft.com/en-us/library/bb895265.aspx#tessellation – including a bunch of pretty diagrams. One of those times when we have a much more complex-looking plan, but just because of the good that’s going on. This tessellation stuff was introduced in SQL Server 2012. But my query isn’t using it. When I try to use the FORCESEEK hint on the Person.Address table, I get the friendly error: Msg 8622, Level 16, State 1, Line 1 Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN. And I’m almost tempted to just give up and move back to the old method of checking increasingly large circles around my location. After all, I can even leverage multiple OUTER APPLY clauses just like I did in my recent Lookup post. WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT     l.Name,     COALESCE(a1.AddressLine1,a2.AddressLine1,a3.AddressLine1),     COALESCE(a1.City,a2.City,a3.City),     s.Name AS [State],     c.Name AS Country FROM MyLocations AS l OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 1000     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a1 OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 5000     AND a1.AddressID IS NULL     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a2 OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 20000     AND a2.AddressID IS NULL     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a3 JOIN Person.StateProvince AS s     ON s.StateProvinceID = COALESCE(a1.StateProvinceID,a2.StateProvinceID,a3.StateProvinceID) JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; But this isn’t friendly-looking at all, and I’d use the method recommended by Isaac Kunen, who uses a table of numbers for the expanding circles. It feels old-school though, when I’m dealing with SQL 2012 (and later) versions. So why isn’t my query doing what it’s supposed to? Remember the query... WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT l.Name, a.AddressLine1, a.City, s.Name AS [State], c.Name AS Country FROM MyLocations AS l CROSS APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a JOIN Person.StateProvince AS s     ON s.StateProvinceID = a.StateProvinceID JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; Well, I just wasn’t reading http://msdn.microsoft.com/en-us/library/ff929109.aspx properly. The following requirements must be met for a Nearest Neighbor query to use a spatial index: A spatial index must be present on one of the spatial columns and the STDistance() method must use that column in the WHERE and ORDER BY clauses. The TOP clause cannot contain a PERCENT statement. The WHERE clause must contain a STDistance() method. If there are multiple predicates in the WHERE clause then the predicate containing STDistance() method must be connected by an AND conjunction to the other predicates. The STDistance() method cannot be in an optional part of the WHERE clause. The first expression in the ORDER BY clause must use the STDistance() method. Sort order for the first STDistance() expression in the ORDER BY clause must be ASC. All the rows for which STDistance returns NULL must be filtered out. Let’s start from the top. 1. Needs a spatial index on one of the columns that’s in the STDistance call. Yup, got the index. 2. No ‘PERCENT’. Yeah, I don’t have that. 3. The WHERE clause needs to use STDistance(). Ok, but I’m not filtering, so that should be fine. 4. Yeah, I don’t have multiple predicates. 5. The first expression in the ORDER BY is my distance, that’s fine. 6. Sort order is ASC, because otherwise we’d be starting with the ones that are furthest away, and that’s tricky. 7. All the rows for which STDistance returns NULL must be filtered out. But I don’t have any NULL values, so that shouldn’t affect me either. ...but something’s wrong. I do actually need to satisfy #3. And I do need to make sure #7 is being handled properly, because there are some situations (eg, differing SRIDs) where STDistance can return NULL. It says so at http://msdn.microsoft.com/en-us/library/bb933808.aspx – “STDistance() always returns null if the spatial reference IDs (SRIDs) of the geography instances do not match.” So if I simply make sure that I’m filtering out the rows that return NULL… …then it’s blindingly fast, I get the right results, and I’ve got the complex-but-brilliant plan that I wanted. It just wasn’t overly intuitive, despite being documented. @rob_farley

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• The View-Matrix and Alternative Calculations

  - by P. Avery

  I'm working on a radiosity processor in DirectX 9. The process requires that the camera be placed at the center of a mesh face and a 'screenshot' be taken facing 5 different directions...forward...up...down...left...right... ...The problem is that when the mesh face is facing up( look vector: 0, 1, 0 )...a view matrix cannot be determined using standard trigonometry functions: Matrix4 LookAt( Vector3 eye, Vector3 target, Vector3 up ) { // The "look-at" vector. Vector3 zaxis = normal(target - eye); // The "right" vector. Vector3 xaxis = normal(cross(up, zaxis)); // The "up" vector. Vector3 yaxis = cross(zaxis, xaxis); // Create a 4x4 orientation matrix from the right, up, and at vectors Matrix4 orientation = { xaxis.x, yaxis.x, zaxis.x, 0, xaxis.y, yaxis.y, zaxis.y, 0, xaxis.z, yaxis.z, zaxis.z, 0, 0, 0, 0, 1 }; // Create a 4x4 translation matrix by negating the eye position. Matrix4 translation = { 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, -eye.x, -eye.y, -eye.z, 1 }; // Combine the orientation and translation to compute the view matrix return ( translation * orientation ); } The above function comes from http://3dgep.com/?p=1700... ...Is there a mathematical approach to this problem? Edit: A problem occurs when setting the view matrix to up or down directions, here is an example of the problem when facing down: D3DXVECTOR4 vPos( 3, 3, 3, 1 ), vEye( 1.5, 3, 3, 1 ), vLook( 0, -1, 0, 1 ), vRight( 1, 0, 0, 1 ), vUp( 0, 0, 1, 1 ); D3DXMATRIX mV, mP; D3DXMatrixPerspectiveFovLH( &mP, D3DX_PI / 2, 1, 0.5f, 2000.0f ); D3DXMatrixIdentity( &mV ); memcpy( ( void* )&mV._11, ( void* )&vRight, sizeof( D3DXVECTOR3 ) ); memcpy( ( void* )&mV._21, ( void* )&vUp, sizeof( D3DXVECTOR3 ) ); memcpy( ( void* )&mV._31, ( void* )&vLook, sizeof( D3DXVECTOR3 ) ); memcpy( ( void* )&mV._41, ( void* )&(-vEye), sizeof( D3DXVECTOR3 ) ); D3DXVec4Transform( &vPos, &vPos, &( mV * mP ) ); Results: vPos = D3DXVECTOR3( 1.5, -6, -0.5, 0 ) - this vertex is not properly processed by shader as the homogenous w value is 0 it cannot be normalized to a position within device space...

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• How should calculations be handled in a document database

  - by Morten

  Ok, so I have a program that basically logs errors into a nosql database. Right now there is just a single model for an error and its stored as a document in the nosql database. Basically I want to summarize across different errors and produce a summary of the "types" of errors that occured. Traditionally in a SQL database the this normalization would work with groupings, sums and averages but in a NoSQL database I assume I need to use mapreduce. My current model seems unfit for the task, how should I change the way I store "models" in order to make statistical analysis easy? Would a NoSQL database even be the right tool for this type of problem? I'm storing things in Google AppEngine's BigTable, so there are some limitations to think of as well.

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• XNA - Moving Background Calculations

  - by Jesse Emond

  Hi, My question is relatively hard to explain(for me, at least), so I'll go one step at a time and just tell me in the comments if it's not clear enough. So I'm making a "Defend Your Castle" type 2D game, where two players own a castle and create units that will move horizontally to try to destroy the opponent's base. Here's a screenshot of the game: The distance between both castles is much bigger in a real game though, bigger than the screen's width actually. Because the distance is bigger than the screen's width, I had to implement a simple 2D camera: Camera2D, which only holds a Location Vector2 (and I always make sure this camera is within the field area). Then, I just move all the game elements(castles, units, health bars) by that location, so that if a unit is at (5, 0), and the camera's location is (5, 0), then the unit's position will be moved by 5 units to the left, making it (0, 0) on the screen. At first, I simply used a static background with mountains and clouds(yeah, those are supposed to be mountains and clouds). Obviously, this looked awful: when you moved the camera, the background would stay immobile. Instead, I'd like to make a moving background, kind of a "scrolling" one. But rather than making a background with the same width as the distance between the castles, I'd like to make one that is a little bit smaller(but still bigger than the screen's width). I thought this would create an effect of "distance" with the background(but it might just look awful, too). Here's the background I'm testing with: I tried different ways, but none of them seems to work. I tried this: float backgroundFieldRatio = BackgroundTexture.Width / fieldWidth;//find the ratio between the background and the field. float backgroundPositionX = -cam.Location.X * backgroundFieldRatio;//move the background to the left When I run this with fieldWith = 1600, BackgroundTexture.Width = 1500 and while looking at the rightmost area, the background is offset to the left by a too big amount, and we can see the black clear color in the back, as you can see here: I hope I explained properly what I'm trying to achieve. Thank you for your time. Note: I didn't know what to look for on Google, so I thought I'd ask here.

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• Timing Calculations for Opengl ES 2.0 draw calls

  - by Arun AC

  I am drawing a cube in OpenGL ES 2.0 in Linux. I am calculating the time taken for each frame using below function #define NANO 1000000000 #define NANO_TO_MICRO(x) ((x)/1000) uint64_t getTick() { struct timespec stCT; clock_gettime(CLOCK_MONOTONIC, &stCT); uint64_t iCurrTimeNano = (1000000000 * stCT.tv_sec + stCT.tv_nsec); // in Nano Secs uint64_t iCurrTimeMicro = NANO_TO_MICRO(iCurrTimeNano); // in Micro Secs return iCurrTimeMicro; } I am running my code for 100 frames with simple x-axis rotation. I am getting around 200 to 220 microsecs per frame. that means am i getting around (1/220microsec = 4545) FPS Is my GPU is that fast? I strongly doubt this result. what went wrong in the code? Regards, Arun AC

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• Hierarchies on Steroids #2: A Replacement for Nested Sets Calculations

  In this sequel to his first "Hierarchies on Steroids" article, SQL Server MVP Jeff Moden shows us how to build a pre-aggregated table that will answer most of the questions that you could ask of a typical hierarchy. Any bets on whether Santa is packin’ a Tally Table in his bag or not? 12 essential tools for database professionalsThe SQL Developer Bundle contains 12 tools designed with the SQL Server developer and DBA in mind. Try it now.

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• Pathfinding with MicroPather : costs calculations with sectors and portals

  - by Adan

  Hello, I'm considering using micropather to help me with pathfinding. I'm not using a discrete map : I'm working in 2d with sectors and portales. However, I'm just wondering what is the best way to compute costs with this library in this context. Just to be more clear about geometrical shapes I'm using : sectors are basically convex polygons, and portals are segments that lies on sector's edge. Micropather exposes a pure virtual Graph class that you must inherate and overrides 3 functions. I understand how pathfinding works, so there's no problem in overriding those functions. Right now, my implementation give me results, i.e I'm able to find a path in my map, but I'm not sure I'm using an optimal solution. For the AdjacentCost method : I just take the distance between sector's centers as the cost. I think a better solution should be to use the portal between the two sectors, compute its center, and then the cost should be : distance( sector A center, portal center ) + distance ( sector B center, portal center ). I'm pretty sure the approximation I'm using with just sector's center is enough for most cases, but maybe with thin and long sectors that are perpendicular, this approximation could mislead the A* algorithm. For the LeastCostEstimate method : I just take the midpoint of the two sectors. So, as you understand, I'm always working with sectors' centers, and it's working fine. And I'm pretty sure there's a better way to work. Any suggestions or feedbacks? Thanks in advance!

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• Building a new cluster for mathematical calculations (Win/Lin)

  - by Muhammad Farhan

  I would like to build a new cluster to perform heavy mathematical calculations in Matlab and Abaqus. One of my friend told me that distributed computing is way faster than parallel computing, which is very true after reading a bit on the internet. However, I have never clustered before. Current workstation I own: Dell Precision T5400 2 x Intel Xeon 2.5 GHz 16 GB RAM (2GB x 8) 1 x Western Digital 1TB HDD 7200 rpm 1 x nVidia Quadro FX4600 768MB GPU 1 x 870W PSU OS: Windows 7 Ultimate 64-bit 2nd WS: I can buy another WS similar configuration to the one I own I am not bothered about OS, I am willing to cluster with either Windows or Linux. However, my software are compatible with windows 64-bit only. Please help me setup a cluster. Thank you.

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• Host data transfer limit calculations and network protocol headers

  - by UpTheCreek

  OK, this might be a really stupid question, but... I'm building a web app that utilises websockets. There's fairly rapid messaging going on, so I've been taking a look at the network traffic with wireshark, to see if there's any way of reducing the amount of data we are sending over the wire, and hence costs. A typical message has approx 150 byte data payload, and according to wireshark the lower layer stuff takes up about: Ethernet: 14 bytes IP: 20 Bytes TCP: 20 Bytes My question is, are these network headers included in data transfer calculations? What about TCP ACK messages? (another 54 bytes according to wireshark) This may seem petty, but because we have so much messaging going on, and because the payload is a similar size to these headers, it's significant.

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• Open Source math library for very higher calculations for J2ME

  - by SamSol

  Is there any Open Source math library for very very higher calculations for J2ME?

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• Performing calculations by subsets of data in R

  - by Vivi

  I want to perform calculations for each company number in the column PERMNO of my data frame, the summary of which can be seen here: > summary(companydataRETS) PERMNO RET Min. :10000 Min. :-0.971698 1st Qu.:32716 1st Qu.:-0.011905 Median :61735 Median : 0.000000 Mean :56788 Mean : 0.000799 3rd Qu.:80280 3rd Qu.: 0.010989 Max. :93436 Max. :19.000000 My solution so far was to create a variable with all possible company numbers compns <- companydataRETS[!duplicated(companydataRETS[,"PERMNO"]),"PERMNO"] And then use a foreach loop using parallel computing which calls my function get.rho() which in turn perform the desired calculations rhos <- foreach (i=1:length(compns), .combine=rbind) %dopar% get.rho(subset(companydataRETS[,"RET"],companydataRETS$PERMNO == compns[i])) I tested it for a subset of my data and it all works. The problem is that I have 72 million observations, and even after leaving the computer working overnight, it still didn't finish. I am new in R, so I imagine my code structure can be improved upon and there is a better (quicker, less computationally intensive) way to perform this same task (perhaps using apply or with, both of which I don't understand). Any suggestions?

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• Reversible numerical calculations in Prolog

  - by user8472

  While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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• Numerical calculations in Prolog

  - by user8472

  While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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• Floating point vs integer calculations on modern hardware

  - by maxpenguin

  I am doing some performance critical work in C++, and we are currently using integer calculations for problems that are inherently floating point because "its faster". This causes a whole lot of annoying problems and adds a lot of annoying code. Now, I remember reading about how floating point calculations were so slow approximately circa the 386 days, where I believe (IIRC) that there was an optional co-proccessor. But surely nowadays with exponentially more complex and powerful CPUs it makes no difference in "speed" if doing floating point or integer calculation? Especially since the actual calculation time is tiny compared to something like causing a pipeline stall or fetching something from main memory? I know the correct answer is to benchmark on the target hardware, what would be a good way to test this? I wrote two tiny C++ programs and compared their run time with "time" on Linux, but the actual run time is too variable (doesn't help I am running on a virtual server). Short of spending my entire day running hundreds of benchmarks, making graphs etc. is there something I can do to get a reasonable test of the relative speed? Any ideas or thoughts? Am I completely wrong? The programs I used as follows, they are not identical by any means: #include <iostream> #include <cmath> #include <cstdlib> #include <time.h> int main( int argc, char** argv ) { int accum = 0; srand( time( NULL ) ); for( unsigned int i = 0; i < 100000000; ++i ) { accum += rand( ) % 365; } std::cout << accum << std::endl; return 0; } Program 2: #include <iostream> #include <cmath> #include <cstdlib> #include <time.h> int main( int argc, char** argv ) { float accum = 0; srand( time( NULL ) ); for( unsigned int i = 0; i < 100000000; ++i ) { accum += (float)( rand( ) % 365 ); } std::cout << accum << std::endl; return 0; } Thanks in advance!

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• Calculations in a table of data

  - by Christian W

  I have a table of data with survey results, and I want to do certain calculations on this data. The datastructure is somewhat like this: ____________________________________________________________________________________ | group |individual | key | key | key | | | |subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey|subkey| | | |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q |q|q|q |q |q |q|q|q | |-------|-----------|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--|-|-|--|--|---|-|-|--| | 1 | 0001 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0002 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 1 | 0003 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0004 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 2 | 0005 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 3 | 0006 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | | 4 | 0007 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 |1|7|5 |1 |3 |1|4|1 | ------------------------------------------------------------------------------------ Excuse my poor ascii skills... So, every individual belongs to a group, and has answered some questions. These questions are always grouped in keys and subkeys. Is there any simple method to calculate averages, deviations and similar based on the groupings. Something like public float getAverage(int key, int individual); float avg = getAverage(5,7); I think what I'm asking is what would be the best way to structure the data in C# to make it as easy as possible to work with? I have started making classes for every entity, but I got confused somewhere and something stopped working. So before I continue along this path, I was wondering if there are any other, better, ways of doing this? (Every individual can also have describing variables, like agegroup and such, but that's not important for the base functionality.) Our current solution does all calculations inline in the queries when requesting the data from the database. This works, but it's slow and the number of queries equals questions * individuals + keys * individuals, which could be alot if individual queries. Any suggestions?

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• What is the right data type for calculations in Java

  - by Raju

  Should we use double or BigDecimal for calculations in Java? How much is the overhead in terms of performance for BigDecimal as compared to double?

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• Vector Calculations in LISP

  - by abidikgubidik

  How can I perform vector calculations in lisp, such as magnitude of a vector, norm of a vector, distance (between two points), dot product, cross product, etc. Thanks.

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• GWT Calendrical Calculations

  - by Kyle Hayes

  We have a GWT application that needs to display various holidays. Is there a library available to do these calendrical calculations? If not, we'll have to do our own that we can ingest a set of rules to. Cheers

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• Values of Integers and Calculations

  - by inferno2991

  Say you have a variable n1 which will be the value of three digits entered how can i then without knowing what exactly will be input split n1 into 3 seperate integers to do futher calculations with?

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• Neo4j Performing shortest path calculations on stored data

  - by paddydub

  I would like to store the following graph data in the database, graph.makeEdge( "s", "c", "cost", (double) 7 ); graph.makeEdge( "c", "e", "cost", (double) 7 ); graph.makeEdge( "s", "a", "cost", (double) 2 ); graph.makeEdge( "a", "b", "cost", (double) 7 ); graph.makeEdge( "b", "e", "cost", (double) 2 ); Then run the Dijskra algorighm from a web servlet, to find shortest path calculations using the stored graph data. Then I will print the path to a html file from the servlet. Dijkstra<Double> dijkstra = getDijkstra( graph, 0.0, "s", "e" );

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• Problem creating calculations 'engine' in two class java calculator

  - by tokee

  i have hit a brick wall whilst attempting to create a two class java calculator but have been unsuccessful so far in getting it working. i have the code for an interface which works and displays ok but creating a seperate class 'CalcEngine' to do the actual calculations has proven to be beyond me. I'd appreciate it if someone could kick start things for me and create a class calcEngine which works with the interface class and allows input when from single button i.e. if one is pressed on the calc then 1 displays onscreen. please note i'm not asking someone to do the whole thing for me as i want to learn and i'm confident i can do the rest including addition subtraction etc. once i get over the obstacle of getting the two classes to communicate. any and all assistance would be very much appreciated. Please see the calcInterface class code below - import java.awt.*; import javax.swing.*; import javax.swing.border.*; import java.awt.event.*; /** *A Class that operates as the framework for a calculator. *No calculations are performed in this section */ public class CalcFrame implements ActionListener { private CalcEngine calc; private JFrame frame; private JTextField display; private JLabel status; /** * Constructor for objects of class GridLayoutExample */ public CalcFrame() { makeFrame(); //calc = engine; } /** * This allows you to quit the calculator. */ // Alows the class to quit. private void quit() { System.exit(0); } // Calls the dialog frame with the information about the project. private void showAbout() { JOptionPane.showMessageDialog(frame, "Group Project", "About Calculator Group Project", JOptionPane.INFORMATION_MESSAGE); } private void makeFrame() { frame = new JFrame("Group Project Calculator"); makeMenuBar(frame); JPanel contentPane = (JPanel)frame.getContentPane(); contentPane.setLayout(new BorderLayout(8, 8)); contentPane.setBorder(new EmptyBorder( 10, 10, 10, 10)); /** * Insert a text field */ display = new JTextField(); contentPane.add(display, BorderLayout.NORTH); //Container contentPane = frame.getContentPane(); contentPane.setLayout(new GridLayout(4, 4)); JPanel buttonPanel = new JPanel(new GridLayout(4, 4)); contentPane.add(new JButton("1")); contentPane.add(new JButton("2")); contentPane.add(new JButton("3")); contentPane.add(new JButton("4")); contentPane.add(new JButton("5")); contentPane.add(new JButton("6")); contentPane.add(new JButton("7")); contentPane.add(new JButton("8")); contentPane.add(new JButton("9")); contentPane.add(new JButton("0")); contentPane.add(new JButton("+")); contentPane.add(new JButton("-")); contentPane.add(new JButton("/")); contentPane.add(new JButton("*")); contentPane.add(new JButton("=")); contentPane.add(new JButton("C")); contentPane.add(buttonPanel, BorderLayout.CENTER); //status = new JLabel(calc.getAuthor()); //contentPane.add(status, BorderLayout.SOUTH); frame.pack(); frame.setVisible(true); } /** * Create the main frame's menu bar. * The frame that the menu bar should be added to. */ private void makeMenuBar(JFrame frame) { final int SHORTCUT_MASK = Toolkit.getDefaultToolkit().getMenuShortcutKeyMask(); JMenuBar menubar = new JMenuBar(); frame.setJMenuBar(menubar); JMenu menu; JMenuItem item; // create the File menu menu = new JMenu("File"); menubar.add(menu); // create the Quit menu with a shortcut "Q" key. item = new JMenuItem("Quit"); item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, SHORTCUT_MASK)); item.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { quit(); } }); menu.add(item); // Adds an about menu. menu = new JMenu("About"); menubar.add(menu); // Displays item = new JMenuItem("Calculator Project"); item.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { showAbout(); } }); menu.add(item); } /** * An interface action has been performed. * Find out what it was and handle it. * @param event The event that has occured. */ public void actionPerformed(ActionEvent event) { String command = event.getActionCommand(); if(command.equals("0") || command.equals("1") || command.equals("2") || command.equals("3") || command.equals("4") || command.equals("5") || command.equals("6") || command.equals("7") || command.equals("8") || command.equals("9")) { int number = Integer.parseInt(command); calc.numberPressed(number); } else if(command.equals("+")) { calc.plus(); } else if(command.equals("-")) { calc.minus(); } else if(command.equals("=")) { calc.equals(); } else if(command.equals("C")) { calc.clear(); } else if(command.equals("?")) { } // else unknown command. redisplay(); } /** * Update the interface display to show the current value of the * calculator. */ private void redisplay() { display.setText("" + calc.getDisplayValue()); } /** * Toggle the info display in the calculator's status area between the * author and version information. */ }

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• CRC32 calculations for png chunk doesn't match the real one

  - by user2507197

  I'm attempting to mimic the function used for creating CRC's in PNG files, I'm using the autodin II polynomial and the source code from: http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/libkern/crc32.c My tests have all been for the IHDR chunk, so my parameters have been: crc - 0xffffffff and 0 (both have been suggested) buff - the address of the IHDR Chunk's type. length - the IHDR Chunk's length + 4 (the length of the chunk's data + the length of the type) I printed the calculated CRC in binary, which I compared to the actual CRC of the chunk. I can see no similarities (little-big endian, reversed bits, XOR'd, etc). This is the data for the IHDR chunk (hexadecimal format): length(big endian): d0 00 00 00 (13) type: 49 48 44 52 data: 00 00 01 77 00 00 01 68 08 06 00 00 00 existing CRC: b0 bb 40 ac If anyone can tell me why my calculations are off, or give me a CRC32 function that will work I would greatly appreciate it. Thank-you!

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• Neo4j Reading data / performing shortest path calculations on stored data

  - by paddydub

  I'm using the Batch_Insert example to insert Data into the database How can i read this data back from the database. I can't find any examples of how i do this. public static void CreateData() { // create the batch inserter BatchInserter inserter = new BatchInserterImpl( "var/graphdb", BatchInserterImpl.loadProperties( "var/neo4j.props" ) ); Map<String,Object> properties = new HashMap<String,Object>(); properties.put( "name", "Mr. Andersson" ); properties.put( "age", 29 ); long node1 = inserter.createNode( properties ); properties.put( "name", "Trinity" ); properties.remove( "age" ); long node2 = inserter.createNode( properties ); inserter.createRelationship( node1, node2, DynamicRelationshipType.withName( "KNOWS" ), null ); inserter.shutdown(); } I would like to store graph data in the database, graph.makeEdge( "s", "c", "cost", (double) 7 ); graph.makeEdge( "c", "e", "cost", (double) 7 ); graph.makeEdge( "s", "a", "cost", (double) 2 ); graph.makeEdge( "a", "b", "cost", (double) 7 ); graph.makeEdge( "b", "e", "cost", (double) 2 ); Dijkstra<Double> dijkstra = getDijkstra( graph, 0.0, "s", "e" ); What is the best method to store this kind data with 10000's of edges. Then run the Dijskra algorighm to find shortest path calculations using the stored graph data.

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