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  • C++ Expression Templates

    - by yCalleecharan
    Hi, I currently use C for numerical computations. I've heard that using C++ Expression Templates is better for scientific computing. What are C++ Expression Templates in simple terms? Are there books around that discuss numerical methods/computations using C++ Expression Templates? In what way, C++ Expression Templates are better than using pure C? Thanks a lot

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  • Logarithmic spacing of FFT bins

    - by Mykel Stone
    I'm trying to do the examples within the GameDev.net Beat Detection article ( http://archive.gamedev.net/archive/reference/programming/features/beatdetection/index.html ) I have no issue with performing a FFT and getting the frequency data and doing most of the article. I'm running into trouble though in the section 2.B, Enhancements and beat decision factors. in this section the author gives 3 equations numbered R10-R12 to be used to determine how many bins go into each subband: R10 - Linear increase of the width of the subband with its index R11 - We can choose for example the width of the first subband R12 - The sum of all the widths must not exceed 1024 He says the following in the article: "Once you have equations (R11) and (R12) it is fairly easy to extract 'a' and 'b', and thus to find the law of the 'wi'. This calculus of 'a' and 'b' must be made manually and 'a' and 'b' defined as constants in the source; indeed they do not vary during the song." However, I cannot seem to understand how these values are calculated...I'm probably missing something simple, but learning fourier analysis in a couple of weeks has left me Decimated-in-Mind and I cannot seem to see it.

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  • Logarithmic spacing of FFT subbands

    - by Mykel Stone
    I'm trying to do the examples within the GameDev.net Beat Detection article ( http://archive.gamedev.net/archive/reference/programming/features/beatdetection/index.html ) I have no issue with performing a FFT and getting the frequency data and doing most of the article. I'm running into trouble though in the section 2.B, Enhancements and beat decision factors. in this section the author gives 3 equations numbered R10-R12 to be used to determine how many bins go into each subband: R10 - Linear increase of the width of the subband with its index R11 - We can choose for example the width of the first subband R12 - The sum of all the widths must not exceed 1024 He says the following in the article: "Once you have equations (R11) and (R12) it is fairly easy to extract 'a' and 'b', and thus to find the law of the 'wi'. This calculus of 'a' and 'b' must be made manually and 'a' and 'b' defined as constants in the source; indeed they do not vary during the song." However, I cannot seem to understand how these values are calculated...I'm probably missing something simple, but learning fourier analysis in a couple of weeks has left me Decimated-in-Mind and I cannot seem to see it.

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  • Parsing mathematical experssions with two values that have parenthesis and minus signs

    - by user45921
    I'm trying to parse equations like these which only has two values or the square root of a certain value from a text file: 100+100 -100-100 -(100)+(-100) sqrt(100) by the minues signs, parenthesis and the operator symbol in the middle and the square root, and I have no idea how to start off... I've got the file part done and the simple calculation parts except that I couldnt get my program to solve the equations in the above. #include <stdio.h> #include <string.h> #include <stdlib.h> #include <math.h> main(){ FILE *fp; char buff[255], sym,sym2,del1,del2,del3,del4; double num1, num2; int ret; fp = fopen("input.txt","r"); while(fgets(buff,sizeof(buff),fp)!=NULL){ char *tok = buff; sscanf(tok,"%lf%c%lf",&num1,&sym,&num2); switch(sym){ case '+': printf("%lf\n", num1+num2); break; case '-': printf("%lf\n", num1-num2); break; case '*': printf("%lf\n", num1*num2); break; case '/': printf("%lf\n", num1/num2); break; default: printf("The input value is not correct\n"); break; } } fclose(fp); } that is what have I written for the other basic operations without parenthesis and the minus sign for the second value and it works great for the simple ones. I'm using a switch method to calculate the add, sub, mul and divide but I'm not sure how to properly use the sscanf function (if I am not using it properly) or if there is another way using a function like strtok to properly parse the parenthesis and the minus signs. Any kind help?

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  • 2D isometric picking

    - by Bikonja
    I'm trying to implement picking in my isometric 2D game, however, I am failing. First of all, I've searched for a solution and came to several, different equations and even a solution using matrices. I tried implementing every single one, but none of them seem to work for me. The idea is that I have an array of tiles, with each tile having it's x and y coordinates specified (in this simplified example it's by it's position in the array). I'm thinking that the tile (0, 0) should be on the left, (max, 0) on top, (0, max) on the bottom and (max, max) on the right. I came up with this loop for drawing, which googling seems to have verified as the correct solution, as has the rendered scene (ofcourse, it could still be wrong, also, forgive the messy names and stuff, it's just a WIP proof of concept code) // Draw code int col = 0; int row = 0; for (int i = 0; i < nrOfTiles; ++i) { // XOffset and YOffset are currently hardcoded values, but will represent camera offset combined with HUD offset Point tile = IsoToScreen(col, row, TileWidth / 2, TileHeight / 2, XOffset, YOffset); int x = tile.X; int y = tile.Y; spriteBatch.Draw(_tiles[i], new Rectangle(tile.X, tile.Y, TileWidth, TileHeight), Color.White); col++; if (col >= Columns) // Columns is the number of tiles in a single row { col = 0; row++; } } // Get selection overlay location (removed check if selection exists for simplicity sake) Point tile = IsoToScreen(_selectedTile.X, _selectedTile.Y, TileWidth / 2, TileHeight / 2, XOffset, YOffset); spriteBatch.Draw(_selectionTexture, new Rectangle(tile.X, tile.Y, TileWidth, TileHeight), Color.White); // End of draw code public Point IsoToScreen(int isoX, int isoY, int widthHalf, int heightHalf, int xOffset, int yOffset) { Point newPoint = new Point(); newPoint.X = widthHalf * (isoX + isoY) + xOffset; newPoint.Y = heightHalf * (-isoX + isoY) + yOffset; return newPoint; } This code draws the tiles correctly. Now I wanted to do picking to select the tiles. For this, I tried coming up with equations of my own (including reversing the drawing equation) and I tried multiple solutions I found on the internet and none of these solutions worked. Trying out lots of solutions, I came upon one that didn't work, but it seemed like an axis was just inverted. I fiddled around with the equations and somehow managed to get it to actually work (but have no idea why it works), but while it's close, it still doesn't work. I'm not really sure how to describe the behaviour, but it changes the selection at wrong places, while being fairly close (sometimes spot on, sometimes a tile off, I believe never more off than the adjacent tile). This is the code I have for getting which tile coordinates are selected: public Point? ScreenToIso(int screenX, int screenY, int tileHeight, int offsetX, int offsetY) { Point? newPoint = null; int nX = -1; int nY = -1; int tX = screenX - offsetX; int tY = screenY - offsetY; nX = -(tY - tX / 2) / tileHeight; nY = (tY + tX / 2) / tileHeight; newPoint = new Point(nX, nY); return newPoint; } I have no idea why this code is so close, especially considering it doesn't even use the tile width and all my attempts to write an equation myself or use a solution I googled failed. Also, I don't think this code accounts for the area outside the "tile" (the transparent part of the tile image), for which I intend to add a color map, but even if that's true, it's not the problem as the selection sometimes switches on approx 25% or 75% of width or height. I'm thinking I've stumbled upon a wrong path and need to backtrack, but at this point, I'm not sure what to do so I hope someone can shed some light on my error or point me to the right path. It may be worth mentioning that my goal is to not only pick the tile. Each main tile will be divided into 5x5 smaller tiles which won't be drawn seperately from the whole main tile, but they will need to be picked out. I think a color map of a main tile with different colors for different coordinates within the main tile should take care of that though, which would fall within using a color map for the main tile (for the transparent parts of the tile, meaning parts that possibly belong to other tiles).

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  • Too Many Files In Debian Linux Folder?

    - by Dave Potts
    I've been using an external USB drive on a Debian server for backup. The drive is formatted as NTFS and mounted with ntsfmount. This was working fine, but I was filling up a directory with lots of files. Eventually the backup failed. When I then tried to look at the directory using ls it reported: ls: reading directory .: Numerical result out of range Looking in syslog, I also saw this: Sep 23 07:35:31 tosh ntfsmount[28040]: Failed to read index block: Numerical result out of range. Is this simply that I've reached the upper limit of number of files in a directory? If so, is there any way to extend the number of allowed files?

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  • Easiest method of creating multiple Word documents with incremental number?

    - by DakotaDusty
    I need to create about 80 Word documents that are identical except for a numerical identifier in the document. The identifier is the same as the document filename, eg. the document named "SN-100.doc" must have the string "SN-100" inside the document text. Each unique document will reside in a folder location given by its unique numerical identifier.For example, the file directory hierarchy will look something like this: /SN001/SN-1.doc /SN002/SN-2.doc . . . /SN080/SN-80.doc What is the easiest and fastest method of doing this?

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  • How to filter a mysql database with user input on a website and then spit the filtered table back to the website? [migrated]

    - by Luke
    I've been researching this on google for literally 3 weeks, racking my brain and still not quite finding anything. I can't believe this is so elusive. (I'm a complete beginner so if my terminology sounds stupid then that's why.) I have a database in mysql/phpmyadmin on my web host. I'm trying to create a front end that will allow a user to specify criteria for querying the database in a way that they don't have to know sql, basically just combo boxes and checkboxes on a form. Then have this form 'submit' a query to the database, and show the filtered tables. This is how the SQL looks in Microsoft Access: PARAMETERS TEXTINPUT1 Text ( 255 ), NUMBERINPUT1 IEEEDouble; // pops up a list of parameters for the user to input SELECT DISTINCT Table1.Column1, Table1.Column2, Table1.Column3,* // selects only the unique rows in these three columns FROM Table1 // the table where this query is happening WHERE (((Table1.Column1) Like TEXTINPUT1] AND ((Table1.Column2)<=[NUMBERINPUT1] AND ((Table1.Column3)>=[NUMBERINPUT1])); // the criteria for the filter, it's comparing the user input parameters to the data in the rows and only selecting matches according to the equal sign, or greater than + equal sign, or less than + equal sign What I don't get: WHAT IN THE WORLD AM I SUPPOSED TO USE (that isn't totally hard)!? I've tried google fusion tables - doesn't filter right with numerical data or empty cells in rows, can't relate tables I've tried DataTables.net, can't filter right with numerical data and can't use SQL without a bunch of indepth knowledge, not even sure it can if you have that.. I've looked into using jQuery with google spreadsheets, doesn't work at all either I have no idea how I'm supposed to build a front end with my database. Every place that looks promising (like zohocreator) is asking for money, and is far too simplified to be able to do the LIKE criteria or SELECT DISTINCT stuff.

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  • How do I choose the scaling factor of a 3D game world?

    - by concept3d
    I am making a 3D tank game prototype with some physics simulation, am using C++. One of the decisions I need to make is the scale of the game world in relation to reality. For example, I could consider 1 in-game unit of measurement to correspond to 1 meter in reality. This feels intuitive, but I feel like I might be missing something. I can think of the following as potential problems: 3D modelling program compatibility. (?) Numerical accuracy. (Does this matter?) Especially at large scales, how games like Battlefield have huge maps: How don't they lose numerical accuracy if they use 1:1 mapping with real world scale, since floating point representation tend to lose more precision with larger numbers (e.g. with ray casting, physics simulation)? Gameplay. I don't want the movement of units to feel slow or fast while using almost real world values like -9.8 m/s^2 for gravity. (This might be subjective.) Is it ok to scale up/down imported assets or it's best fit with a world with its original scale? Rendering performance. Are large meshes with the same vertex count slower to render? I'm wondering if I should split this into multiple questions...

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  • Javascript: Machine Constants Applicable?

    - by DavidB2013
    I write numerical routines for students of science and engineering (although they are freely available for use by anybody else as well) and am wondering how to properly use machine constants in a JavaScript program, or if they are even applicable. For example, say I am writing a program in C++ that numerically computes the roots of the following equation: exp(-0.7x) + sin(3x) - 1.2x + 0.3546 = 0 A root-finding routine should be able to compute roots to within the machine epsilon. In C++, this value is specified by the language: DBL_EPSILON. C++ also specifies the smallest and largest values that can be held by a float or double variable. However, how does this convert to JavaScript? Since a Javascript program runs in a web browser, and I don't know what kind of computer will run the program, and JavaScript does not have corresponding predefined values for these quantities, how can I implement my own version of these constants so that my programs compute results to as much accuracy as allowed on the computer running the web browser? My first draft is to simply copy over the literal constants from C++: FLT_MIN: 1.17549435082229e-038 FLT_MAX: 3.40282346638529e+038 DBL_EPSILON: 2.2204460492503131e-16 I am also willing to write small code blocks that could compute these values for each machine on which the program is run. That way, a supercomputer might compute results to a higher accuracy than an old, low-level, PC. BUT, I don't know if such a routine would actually reach the computer, in which case, I would be wasting my time. Anybody here know how to compute and use (in Javascript) values that correspond to machine constants in a compiled language? Is it worth my time to write small programs in Javascript that compute DBL_EPSILON, FLT_MIN, FLT_MIN, etc. for use in numerical routines? Or am I better off simply assigning literal constants that come straight from C++ on a standard Windows PC?

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  • Creating an equation in a word 2003 document using a marco (or through the API)

    - by Sambatyon
    I think the title is fully descriptive. Anyway, I need to generate a word document from my delphi application. It needs to choose from one of four different equations (with some specific parameters for each document). So far I have manage to create the whole document programmatically except the equation. Is it possible to create equations programmatically? if so, where is de API documentation from MS? if not, which solution can be used?

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  • Diophantine Equation [closed]

    - by ANIL
    In mathematics, a Diophantine equation (named for Diophantus of Alexandria, a third century Greek mathematician) is a polynomial equation where the variables can only take on integer values. Although you may not realize it, you have seen Diophantine equations before: one of the most famous Diophantine equations is: X^n+Y^n=Z^n We are not certain that McDonald's knows about Diophantine equations (actually we doubt that they do), but they use them! McDonald's sells Chicken McNuggets in packages of 6, 9 or 20 McNuggets. Thus, it is possible, for example, to buy exactly 15 McNuggets (with one package of 6 and a second package of 9), but it is not possible to buy exactly 16 nuggets, since no non- negative integer combination of 6's, 9's and 20's adds up to 16. To determine if it is possible to buy exactly n McNuggets, one has to solve a Diophantine equation: find non-negative integer values of a, b, and c, such that 6a + 9b + 20c = n. Problem 1 Show that it is possible to buy exactly 50, 51, 52, 53, 54, and 55 McNuggets, by finding solutions to the Diophantine equation. You can solve this in your head, using paper and pencil, or writing a program. However you chose to solve this problem, list the combinations of 6, 9 and 20 packs of McNuggets you need to buy in order to get each of the exact amounts. Given that it is possible to buy sets of 50, 51, 52, 53, 54 or 55 McNuggets by combinations of 6, 9 and 20 packs, show that it is possible to buy 56, 57,..., 65 McNuggets. In other words, show how, given solutions for 50-55, one can derive solutions for 56-65. Problem 2 Write an iterative program that finds the largest number of McNuggets that cannot be bought in exact quantity. Your program should print the answer in the following format (where the correct number is provided in place of n): "Largest number of McNuggets that cannot be bought in exact quantity: n" Hints: Hypothesize possible instances of numbers of McNuggets that cannot be purchased exactly, starting with 1 For each possible instance, called n, a. Test if there exists non-negative integers a, b, and c, such that 6a+9b+20c = n. (This can be done by looking at all feasible combinations of a, b, and c) b. If not, n cannot be bought in exact quantity, save n When you have found six consecutive values of n that in fact pass the test of having an exact solution, the last answer that was saved (not the last value of n that had a solution) is the correct answer, since you know by the theorem that any amount larger can also be bought in exact quantity

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  • Creating an Equation Editor 3.0 equation in a Word 2003 document using a marco (or through the API)

    - by Sambatyon
    I think the title is fully descriptive now. Anyway, I need to generate a word document from my delphi application. It needs to choose from one of four different equations (with some specific parameters for each document). So far I have manage to create the whole document programmatically except the equation. Is it possible to create equations programmatically? if so, where is de API documentation from MS? if not, which solution can be used?

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  • Efficient algorithm to generate all solutions of a linear diophantine equation with ai=1

    - by Ben
    I am trying to generate all the solutions for the following equations for a given H. With H=4 : 1) ALL solutions for x_1 + x_2 + x_3 + x_4 =4 2) ALL solutions for x_1 + x_2 + x_3 = 4 3) ALL solutions for x_1 + x_2 = 4 4) ALL solutions for x_1 =4 For my problem, there are always 4 equations to solve (independently from the others). There are a total of 2^(H-1) solutions. For the previous one, here are the solutions : 1) 1 1 1 1 2) 1 1 2 and 1 2 1 and 2 1 1 3) 1 3 and 3 1 and 2 2 4) 4 Here is an R algorithm which solve the problem. library(gtools) H<-4 solutions<-NULL for(i in seq(H)) { res<-permutations(H-i+1,i,repeats.allowed=T) resum<-apply(res,1,sum) id<-which(resum==H) print(paste("solutions with ",i," variables",sep="")) print(res[id,]) } However, this algorithm makes more calculations than needed. I am sure it is possible to go faster. By that, I mean not generating the permutations for which the sums is H Any idea of a better algorithm for a given H ?

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  • Function pointer arrays in Fortran

    - by Eduardo Dobay
    I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn't let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a program for solving a system of differential equations, so I could input the equations without having a million parameters in my subroutines.)

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  • How to best integrate generated code

    - by Arne
    I am evaluating the use of code generation for my flight simulation project. More specifically there is a requirement to allow "the average engineer" (no offense I am one myself) to define the differential equations that describe the dynamic system in a more natural syntax than C++ provides. The idea is to devise a abstract descriptor language that can be easily understood and edited to generate C++ code from. This descriptor is supplied by the modeling engineer and used by the ones implementing and maintaining the simulation evironment to generate code. I've got something like this in mind: model Aircraft has state x1, x2; state x3; input double : u; input bool : flag1, flag2; algebraic double : x1x2; model Engine : tw1, tw2; model Gear : gear; model ISA : isa; trim routine HorizontalFight; trim routine OnGround, General; constant double : c1, c2; constant int : ci1; begin differential equations x1' = x1 + 2.*x2; x2' = x2 + x1x2; begin algebraic equations x1x2 = x1*x2 + x1'; end model It is important to retain the flexibility of the C language thus the descriptor language is meant to only define certain parts of the definition and implementation of the model class. This way one enigneer provides the model in from of the descriptor language as examplified above and the maintenance enigneer will add all the code to read parameters from files, start/stop/pause the execution of the simulation and how a concrete object gets instatiated. My first though is to either generate two files from the descriptor file: one .h file containing declarations and one .cpp file containing the implementation of certain functions. These then need to be #included at appropriate places [File Aircarft.h] class Aircraft { public: void Aircraft(..); // hand-written constructor void ReadParameters(string &file_name); // hand-written private: /* more hand wirtten boiler-plate code */ /* generate declarations follow */ #include "Aircraft.generated.decl" }; [File Aircraft.cpp] Aircarft::Aircraft(..) { /* hand-written constructer implementation */ } /* more hand-written implementation code */ /* generated implementation code follows */ #include "Aircraft.generated.impl" Any thoughts or suggestions?

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  • Inserting equation numbers macro

    - by krzych
    I want to insert equations into Word 2010. I'm inserting the center-aligned equations and then want to add a number to the same line, which will be aligned to the right hand side of the page. I'm having a problem with setting the alignment of the number to the right with equation aligned to center. My code is currently only inserting the number without the correct alignment: Sub EqnNumber() Selection.TypeText Text:="(" Selection.Fields.Add Range:=Selection.Range, Type:=wdFieldEmpty, _ Text:="STYLEREF \s ""Naglówek 1"" ", PreserveFormatting:=True Selection.TypeText Text:="." Selection.Fields.Add Range:=Selection.Range, Type:=wdFieldEmpty, _ Text:="SEQ Rysunek \* ARABIC \s 1", PreserveFormatting:=True Selection.TypeText Text:=")" End Sub

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  • Calculating a parabola: What am I doing wrong? [closed]

    - by Nils
    I was following this thread and copied the code in my project. Playing around with it turns out that it seems not to be very precise. Recall the formula: y = ax^2 + bx +c Since the first given point I have is at x1 = 0, we already have c=y1 . We just need to find a and b. Using: y2 = ax2^2 + bx2 +c y3 = ax3^2 + bx3 +c Solving the equations for b yields: b = y/x - ax - cx Now setting both equations equal to each other so b falls out y2/x2 - ax2 - cx2 = y3/x3 - ax3 - cx3 Now solving for a gives me: a = ( x3*(y2 - c) + x2*(y3 - c) ) / ( x2*x3*(x2 - x3) ) (is that correct?!) And then using again b = y2/x2 - ax2 - cx2 to find b. However so far I haven't found the correct a and b coeffs. What am I doing wrong?

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  • What math should all game programmers know?

    - by Tetrad
    Simple enough question: What math should all game programmers have a firm grasp of in order to be successful? I'm not specifically talking about rendering math or anything in the niche areas of game programming, more specifically just things that even game programmers should know about, and if they don't they'll probably find it useful. Note: as there is no one correct answer, this question (and its answers) is a community wiki. Also, if you would like fancy latex math equations, feel free to use http://mathurl.com/.

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  • Why use other number bases when programming

    - by JMD
    My coworkers and I have been bending our minds to figuring out why anyone would go out of their way to program numbers in a base other than base 10. I suggested that perhaps you could optimize longer equations by putting the variables in the correct base you are working with (for instance, if you have only sets of 5 of something with no remainders you could use base 5), but I'm not sure if that's true. Any thoughts?

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  • how to solve the error: The name in the tag element must match the element type in the start tag

    - by user2227801
    please I am working on a very important large word document file it contains many math equations and suddenly i cant open that file it keep giving me an error : The name in the tag element must match the element type in the start tag. Location : Part: /word/document.xml, Line: 2, Column 5437966 I uploaded my file in http://www.freeuploadsite.com/do.php?id=19094 Please help me. Please save me. Thanks in advance

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  • Why use other bases when programming [closed]

    - by JMD
    Possible Duplicate: Why use other number bases when programming My coworkers and I have been bending our minds to figuring out why anyone would go out of their way to program numbers in a base other than base 10. I suggested that perhaps you could optimize longer equations by putting the variables in the correct base you are working with (for instance, if you have only sets of 5 of something with no remainders you could use base 5), but I'm not sure if that's true. Any thoughts?

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  • Correct permutation cycle for Verhoeff algorithm

    - by James
    Hello, I'm implementing the Verhoeff algorithm for a check digit scheme, but there seems to be some disagreement in web sources as to which permutation cycle should form the basis of the permutation table. Wikipedia uses: (36)(01589427) while apparently, Numerical Recipies uses a different cycle and this book uses: (0)(14)(23)(56789), quoted from a 1990 article by Winters. It also notes that Verhoeff used the one Wikipedia quotes. Now, my number theory is a little rusty, but the Wikipedia cycle clearly will repeat after the 8th power, while the book one will take 10, despite it saying that s^8=s. Table 2.14(b) has other errors in the 2-cycles, so this is dubious anyway. Unfortunately, I don't have copies of the original articles (and am too tight to pay/disgusted that 40-year old knowledge is still being held to ransom by publishers), nor a copy of Numerical Recipes to check (and am loath to install their paranoia-induced copy protection plug-in to view online). So does any one know which is correct? Are they both correct?

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