REALLY WEIRED ISSUE

[Gaurav Malhotra]

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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