Calculation of Phi value in matlab

width=20;
length=40;
height=10;

x=1:2:20;
y=1:4:40;
z=1:1:10;

E =length/width;
alpha=atan(E);
x1= (x.*sin(alpha)) - (y .* cos (alpha));
y1= (height./2)-z;
k= y1 ./ x1;
phi1=zeros(size(k)); 
for ii= 1:length(k)
    if k(ii)>0
        phi1(ii)= atan(k(ii));           % equation 1
    else
        phi1(ii)= pi-atan(k(ii));        % equation 2     
    end
end

Error msg : ??? Subscript indices must either be real positive integers or logicals.

Sorry. I am very noob at matlab. Please help me correct with the error. I am trying to calculate the phi1 value. When k is positive it have to use the quation 1 and when k is negative it have to use the equation 2.

Answer 1

[maria]

Try:

width=20;length=40;height=10;

x=1:2:20; 
y=1:4:40; 
z=1:1:10; 
E =length/width; 
alpha=atan(E); 
x1= (x.*sin(alpha)) - (y .* cos (alpha)); 
y1= (height./2)-z; 
k= y1 ./ x1; 
[M,N]=size(k)
phi1=zeros(N); 
for ii= 1:N
    if k(ii)>0 phi1(ii)= atan(k(ii)); % equation 1 else phi1(ii)= pi-atan(k(ii)); % equation 2 
    end
end

[unknown777]

Thanks....

Answer 2

[Image Analyst]

This error is very well explained by the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F After reading that, you will know what to do.

[unknown777]

Thanks..