How to write a function in MATLAB?

Hello

i need to write this function using matlab

where theta takes the range of values ( 0 to 80 step 1) and the frequncy (f) take the values (18 to 22 ) and the other parameters are fixed

then i need to plot the result with the values of frequency (x-axis include the frequency and y-axis include the G)

i tried to execute it for one values of (theta and f) using this code

gain_mag=sin(N*pi/2*sin(theta)*(freq/fc-1))/sqrt(N)*sin(pi/2*sin(theta)*(freq/fc-1));
gain_phase=exp(j*0.5*(N-1)*pi*sin(theta)*(freq/fc-1));
gain=gain_mag*gain_phase;
plot(gain);
grid on;

how can i execute it for different values of theta and f?

Answer 1

[Walter Roberson]

theta = (0:80).';   %column vector
freq = 18:22;       %row vector

gain_mag = sin(pi/2 .* N .* sin(theta) .* (freq/fc-1)) ./ sqrt(N) .* sin(pi/2 .* sin(theta) .* (freq/fc-1));
gain_phase = exp(1j*pi/2 .* (N-1) .* sin(theta) .* (freq/fc-1));
gain = gain_mag .* gain_phase;

surf(freq, theta, gain)

There are two tricks here:

1. Use element-by-element operators such as .* because you are going to be multiplying and dividing non-scalars
2. Use a row vector for one of the variables and a column vector for the other one, and starting R2015b MATLAB will automatically expand that into grids of calculations. If you are using an earlier version, you would want to use meshgrid() to make theta and freq 2D grids of values.