how do i get rid of the fractions on array calculations

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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

Answers (2)

Roger Stafford
Roger Stafford on 1 Oct 2014
Edited: Roger Stafford on 1 Oct 2014
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'.
  2 Comments
the cyclist
the cyclist on 1 Oct 2014
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
Roger Stafford on 1 Oct 2014
You are right Cyclist. The way I had it originally was correct, so I have corrected the correction.

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the cyclist
the cyclist on 1 Oct 2014
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)

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