error - "Attempted to access w(0.000542549); index must be a positive integer or logical."

I am writing a code to find the gain of a tranversal filter. I am getting the error - "Attempted to access w(0.000542549); index must be a positive integer or logical." The code is shown below:

del_L = 10;
del_Lambda = 1550*10^(-9);
D = 35;
rho_D = D*del_L*del_Lambda
% n_Lambda = input('Enter the refractive index of the fiber core');
n_Lambda = 1.46;
c = 3*10^8;%Speed of light
rho_d = (del_L*n_Lambda)/c;
a = rho_d+rho_D
for f=8:0.1:12.5
    w = abs(2*3.14*f)
    H0 = mod(1+cos(w(rho_d+rho_D)),0)/2
end

Please help!

Answer 1

[Robert]

Just before your final end statement you have the line

H0 = mod(1+cos(w(rho_d+rho_D)),0)/2

The error occurs when MATLAB tries to index into the variable w in your statement w(rho_d+rho_D). I bet you didn't mean to index into w. If you meant to multiply the two expressions, you need an asterisk.

H0 = mod(1+cos(w*(rho_d+rho_D)),0)/2

[Rohith Ramaiah]

Thank you for the answer. How can I express the equation: H(w) = 1+cos[w(rho_D+rho_d)]/2 with w *(omega) running through the frequencies 8-12.5 Ghz.

[Robert]

MATLAB is great at this kind of computation (among others). Instead of the for loop, you can vectorize your computation (a MATLAB term referring to exactly what we are doing: accelerating code by trading loops for vector math).

Instead of assigning f as the iterator of the loop, let's make it the whole loop vector.

f = 8:0.1:12.5; % a row vector of all your f values

Then we can operate on the vector. You have to be careful when you have multiple vectors, but in your case, all your other values are scalars so the code is pretty foolproof.

w = abs(2*pi*f); % just like before, but with MATLAB's built-in value for pi
H = 1 + cos(w*(rho_D+rho_d))/2; % or cosd for inputs in degrees

Just a heads up: did you mean (1 + cos(...) )/2 as in your original code or 1 + cos(...)/2 as in your comment?