If loop giving me troubles

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Thomas
Thomas on 30 Apr 2015
Commented: Nobel Mondal on 30 Apr 2015

So I'm trying to stop certain parts of my code if the matrix values are between -1 and 1, but it won't stop there... I'm using an if statement, and just can't figure out where I'm going wrong. Here is my code:

i = 1;
dh = [0.01:0.01:50];
for j = 1:length(dh)
        Ortho_heights=[-(.7+dh(j)) -.7 0 .7  .7+dh(j)];
        fprintf('\nGLARE, [45/-45/-45/45]\n\n');
        fprintf('\nA Matrix\n');
        A(:,:,i) = (Ortho_heights(2) - Ortho_heights(1)).*Qbar(:,:,i) + ...
               (Ortho_heights(3) - Ortho_heights(2)).*Qbar(:,:,i+1) + ...
               (Ortho_heights(4) - Ortho_heights(3)).*Qbar(:,:,i+2) + ...
               (Ortho_heights(5) - Ortho_heights(4)).*Qbar(:,:,i+3);
        display(A(:,:,i));
        fprintf('\nB Matrix\n');
        B(:,:,i) = (1/2)*...
        ((((Ortho_heights(2)).^2 - (Ortho_heights(1)).^2)).*Qbar(:,:,i) + ...
        (((Ortho_heights(3)).^2 - (Ortho_heights(2)).^2)).*Qbar(:,:,i+1) + ...
        (((Ortho_heights(4)).^2 - (Ortho_heights(3)).^2)).*Qbar(:,:,i+2) + ...
        (((Ortho_heights(5)).^2 - (Ortho_heights(4)).^2)).*Qbar(:,:,i+3));
        if B(:,:,i) < 1*10^-6
            B(:,:,i) = 0;
        end
        display(B(:,:,i));
        fprintf('\nD Matrix\n')
        D(:,:,i) = (1/3)*...
        ((((Ortho_heights(2)).^3 - (Ortho_heights(1)).^3)).*Qbar(:,:,i) + ...
        (((Ortho_heights(3)).^3 - (Ortho_heights(2)).^3)).*Qbar(:,:,i+1) + ...
        (((Ortho_heights(4)).^3 - (Ortho_heights(3)).^3)).*Qbar(:,:,i+2) + ...
        (((Ortho_heights(5)).^3 - (Ortho_heights(4)).^3)).*Qbar(:,:,i+3));
%     && (-1 < D(2,3,i)) && (D(2,3,i) < 1)
        if (-1 < D(1,3,i)) && (D(1,3,i) < 1)
            flag == 1;
        else
            flag == 0;       
        end
        if flag == 1
            break
        end
end

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Accepted Answer

Nobel Mondal
Nobel Mondal on 30 Apr 2015
I agree with the previous comments. However, your problem is with the inappropriate use of assignment operator in the if-else loop.
Try this:
if (-1 < D(1,3,i)) && (D(1,3,i) < 1)
flag = 1; % Not ==
else
flag = 0;
end
  2 Comments
Thomas
Thomas on 30 Apr 2015
Thank you! Another syntax error keeps me up all night. :(
Nobel Mondal
Nobel Mondal on 30 Apr 2015
I guess, we all have been there sometimes :)
I would also suggest the same thing as Thorsten mentioned in his answer. Try the break statement within the if block itself to avoid similar situation, if possible:
if (-1 < D(1,3,i)) && (D(1,3,i) < 1)
break
end

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More Answers (2)

Thorsten
Thorsten on 30 Apr 2015
Edited: Thorsten on 30 Apr 2015
Your for loop uses j but in the if clause you check for i, which is always 1. Is that really what you intended to do? If so, your testvalue D(1,3,1) may never be within the limits.
BTW, you could write your code more succinctly as
testvalue = D(1,3,i);
if testvalue > -1 && testvalue < 1
break
end
Image Analyst
Image Analyst on 30 Apr 2015
Before the if, add these lines:
fprintf('D(2,3,%d) = %f\n', i, D(2,3,i));
fprintf('D(1,3,%d) = %f\n', i, D(1,3,i)); % Whichever row you want - 2 or 1.
and see what values of D it spits out to the command window. It must not be getting into that range. Otherwise give us Qbar so we can run your code.

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