i can get the equation to give a matrix 82x96

for f=1:0.2:20;

   ti=length(f);
      T=(1/4*pi*f)*atan(sum(sin(4*pi*f*ti))/sum(cos(4*pi*f*ti)));
      P(f)=(sum(d18ored*sin(2*pi*f.*(ti-T)).^2))/(sum(sin(2*pi*f.*(ti-T).^2)))...
          +(sum(d18ored*cos(2*pi*f.*(ti-T)))).^2/(sum(cos(2*pi*f.*(ti-T)).^2));
plot(P(f),f) 
end

d18ored is a matrix 82x1 it is suppose to give me a 82x96 and gives me a error.

"Subscript indices must either be real positive integers or logicals."

[João Bernardo]

In an assignment A(I) = B, the number of elements in B and I must be the same. now i got this error

Answer 1

[Thorsten]

f takes values 1, 1.2, 1.4, ... 20, and you try to use f as subscript

P(f)

which is not allowed.

You can use

fvec = 1:0.2:20;
for i = 1:numel(fvec)
   f = fvec(i);
   T = ...
   P(i) = ...
end