how do i get rid of the fractions on array calculations

for X=1:0.1:64;

   for  Y=1:0.1:64

vble(X,Y)=-0.5*sin(X*2*3.14/64*sin(Y*2*3.14/64);

if vble(X,Y)==psisecondsecond1;

 vble(X,Y)=psisecondsecond1;

else

    vble=0;

end

   end

end

I want to know how i can store the values of vble that are calculated for the fractional values of X and Y. Like how do i store vble(1.1,5.5). i know matlab cant store fractions but i am not able to write out a for loop for my required needs. Thanks, Ananth

Answer 1

[Roger Stafford]

You need to proceed differently in your for loops.

   n = 631;
   for ix = 1:n
     X = .1*(ix-1)+1;
     for iy = 1:n
       Y = .1*(iy-1)+1;
       vble(ix,iy)=-0.5*sin(X*2*3.14/64*sin(Y*2*3.14/64);
       % (Correction corrected)
       ....

Another point to make here is that you are demanding exact equality when you write

   vble(X,Y)==psisecondsecond1

but since your computation involves the sine function, round-off errors may convert exact equalities into close approximations. Instead you should write

   abs(vble(X,Y)-psisecondsecond1)<tol

for some very small value 'tol'.

[the cyclist]

Roger, is your correction correct? I see you are using both X(ix) and Y*(iy). I did not dig into the details, but I'm just guessing from symmetry that one of those is not what you intended.

[Roger Stafford]

You are right Cyclist. The way I had it originally was correct, so I have corrected the correction.

Answer 2

[the cyclist]

I typically do this as follows:

X=1:0.1:64;
numberOfX = numel(X);

Y=1:0.1:64;
numberOfY = numel(Y);

for nx = 1:numberOfX
for ny = 1:numberOfY
    vble(nx,ny) = ...
end
end

Inside the for loop, you'll need to reference X and Y by indices:

X(nx)
Y(ny)