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Re: REALLY WEIRED ISSUE

 From: Doug Stewart Subject: Re: REALLY WEIRED ISSUE Date: Tue, 26 Feb 2008 15:49:07 -0500 User-agent: Thunderbird 1.5.0.14 (Windows/20071210)

Gaurav Malhotra wrote:

*Here it is, inherently the same code I just made few changes to make some variables to be input by user, Thanks a ton for your help.*

#include <iostream>
#include <math.h>
#include <fstream>

double GFactorTopWall(double x, int y, int n, int e, int z)
{
double PI = 3.14159265;
double a = (y - n);
double b = (x - e);
double asquared = a * a;
double bsquared = b * b;
double zsquared = z * z;

double g1 = (a * sqrt(bsquared + zsquared));
double g2 = atan( (a / sqrt(bsquared + zsquared)));
double g3 = (b * sqrt(asquared + zsquared));
double g4 = atan( (b / sqrt(asquared + zsquared)));
double g5 = zsquared / 2;
double g6 = log(bsquared + asquared + zsquared);
double g7 = 2 * PI;
double GValue;
GValue = ((g1 * g2) + (g3 * g4) - (g5 * g6))/g7;
return GValue;
}

int main()
{
int y = {0, 30};
int n = {0, 30};
int e = {0, 10};
The difference is above
you have [0,30] in Octave

int z = 4;
double x;
double minusone;
double FValueTopWall;
double GValueTopWall;
double sum = 0;
int minwidthinch = 36;
int maxwidthinch = 62;
int furnacewidthinch = 120;
std::cout << "\n\n Calulating view factors and writing them to a file too ##### \n\n";

std::ofstream FValueFile("f-top-wall.txt");

double loop = minwidthinch;

do
{
x = (furnacewidthinch - loop) / (2 * 12);
x = (((furnacewidthinch - loop)/2) + loop) / 12;
double area = (x - x) * (y - y); std::cout << "\nFor a Strip Width of " << loop << " inches : - \n"; std::cout << "+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+\n\n"; FValueFile << "\nFor a Strip Width of " << loop << " inches : - \n"; FValueFile << "+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+\n\n";

sum = 0;

for (int l = 0 ; l < 2; ++l)
{
for (int k = 0; k < 2; ++k)
{
for (int j = 0; j < 2; ++j)
{
for (int i = 0; i < 2; ++i)
{
minusone = pow((double)-1, ((i+1) + (j+1) + (k+1) + (l+1))); GValueTopWall = GFactorTopWall(x[i], y[j], n[k], e[l], z); sum += (minusone * GValueTopWall);
}
}
}
}

FValueTopWall = sum/area;

std::cout << "Top Wall View-factor @ y(" << y << "," << y << ") = " << FValueTopWall << "\n"; FValueFile << "Top Wall View-factor @ y(" << y << "," << y << ") = " << FValueTopWall << "\n";

loop = loop + 2;
}
while (loop <= maxwidthinch);

FValueFile.close();

std::cout << "\n";
return 0; }

02/26/2008 03:10 PM

To
cc
Subject
Re: REALLY WEIRED ISSUE

Gaurav Malhotra wrote:
>
> Hi All,
>
> This is my first post to this mailing list and I am trying to use
> octave to promote it at my work for adoption as primary for scientific
> stuff.
> ALSO APOLOGIES FOR A REALLY LONG MESSAGE.
>
> My main issue is, Below is the code I wrote in octave(a rather simple
> one) but it dows not give me the correct answer. I have debugged this
> several time and have tried to do as many things I could think of but
> the solution I get is inaccurate. Than I wrote exactly the same code
> in C/C++  and got the right solution in first go.
>
> *Could you all help me with what's wrong in the code as I really need
> "octave" to work for me cause it's so much better than using C/C++ for
> such stuff. *FYI, I am using Octave 3.0 on windows and SciTe as my
> editor.
>
>
> Below is my code: -
>
> +++++++++++++++++++++++++++
>
> # Function Definition here
>
> function GValueTopWall = GFactorTopWall(x, y, n, e, z)
>   a = y - n;
>   b = x - e;
>   asquared = a * a;
>   bsquared = b * b;
>   zsquared = z * z;
>   GValueTopWall = 0;
> > g1 = (a * sqrt(bsquared + zsquared));
>   g2 = atan( ( a / sqrt(bsquared + zsquared)) );
>   g3 = (b * sqrt(asquared + zsquared));
>   g4 = atan( (b / sqrt(asquared + zsquared)) );
>   g5 = zsquared / 2;
>   g6 = log(bsquared + asquared + zsquared);
>   g7 = 2 * pi;
> > GValueTopWall = ((g1 * g2) + (g3 * g4) - (g5 * g6))/g7;
>   return;
> endfunction
>
> # Actual Code Starts Here
> # Assumptions: -
> # Furnace Depth/Length = 30 ft
> # Furnace Height = 8 ft
> # Furnace Width = 10 ft
> # Strip width min = 36in/3ft max = 62in/5.166ft with 2in/0.16ft step
>
> clc
>
> y = [0, 30];
> n = [0, 30];
> e = [0, 30];
> z = 4;
> sum = 0;
> minwidthinch = 36;
> maxwidthinch = 62;
> furnacewidthinch = 120;
> loop = minwidthinch;
>
> do
>   x(1) = (furnacewidthinch - loop) / (2 * 12);
>   x(2) = (((furnacewidthinch - loop) / 2) + loop) / 12;
> > area = (x(2) - x(1)) * (y(2) - y(1));
>   sum = 0;
>   for l = 1:2
>     for k = 1:2
>       for j = 1:2
>         for i = 1:2
>           minusone = (-1)^(i + j + k + l);
>           GValueTopWall = GFactorTopWall(x(i), y(j), n(k), e(l), z);
>           sum = sum + (minusone * GValueTopWall)/area;
>         endfor
>       endfor
>     endfor
>   endfor
> > FValueTopWall = sum;
>   printf("View Factor for %d strip width = %f \n", loop, FValueTopWall);
>   loop = loop + 2;
> until (loop > maxwidthinch)
>
> ++++++++++++++++++++++++++++++++++++++
>
> Output of this code: -
>
> >C:\Program Files\Octave\bin\octave.exe -q "view-factors-topwall.m"
>  - Use `pkg list' to see a list of installed packages.
>  - SciTE editor installed. Use `edit' to start the editor.
>  - MSYS shell available (C:\Program Files\Octave\msys).
>  - Graphics backend: jhandles.
>
>
> View Factor for 36 strip width = 0.784004
> View Factor for 38 strip width = 0.783552
> View Factor for 40 strip width = 0.783074
> View Factor for 42 strip width = 0.782569
> View Factor for 44 strip width = 0.782037
> View Factor for 46 strip width = 0.781479
> View Factor for 48 strip width = 0.780893
> View Factor for 50 strip width = 0.780279
> View Factor for 52 strip width = 0.779637
> View Factor for 54 strip width = 0.778967
> View Factor for 56 strip width = 0.778269
> View Factor for 58 strip width = 0.777542
> View Factor for 60 strip width = 0.776786
> View Factor for 62 strip width = 0.776000
> >Exit code: 0
>
> Correct Solution: -
>
> View factor for 36 inch strip width = 0.697687
> View factor for 38 inch strip width = 0.696786
> View factor for 40 inch strip width = 0.695833
> View factor for 42 inch strip width = 0.694826
> View factor for 44 inch strip width = 0.693767
> View factor for 46 inch strip width = 0.692653
> View factor for 48 inch strip width = 0.691485
> View factor for 50 inch strip width = 0.690262
> View factor for 52 inch strip width = 0.688984
> View factor for 54 inch strip width = 0.687649
> View factor for 56 inch strip width = 0.686257
> View factor for 58 inch strip width = 0.684808
> View factor for 60 inch strip width = 0.6833
> View factor for 62 inch strip width = 0.681735
>
> >
> Thanks in advance
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I have looked at this and tested atan2 instead of atan and I tried log10
instead of log but these did not help.
If you send me your "C" code I might be able to see what is different.

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