Plotting magnitude of complex expression

The code I have used is as follows:

%Define constants
A_1=1;
A_2=2;
L=1;

%Specify range of k values to plot on x axis
k=[0:1:10];

%complex function to plot
t=(2*(A_1*A_2*cos(L*k) + A_1*A_2*sin(L*k)*1i))/(sin(L*k)*A_1^2*1i + 2*cos(L*k)*A_1*A_2 + sin(L*k)*A_2^2*1i);

%Finding magnitude of complex values
U=abs(t);

%Plot curve of U over specified range of k
plot(k,U);

I am looking to plot a graph of U on the y-axis, with k varying between 0 and 10 on the x axis. Having generated a matrix k of 11 integer values, the function t is only evaluated as a single complex number, rather than a matrix of complex numbers for each of the 11 input values of k. This means that the graph cannot be plotted since only a single point is generated.

Is there a mistake in my code which leads to t being a single value, rather than a range of values for varying k, which can then be plotted?

Many thanks for your help.

Answer 1

[the cyclist]

The reason t ends up as a single value is that you inadvertently did a matrix division in your calculation. Try this instead:

%Define constants
A_1=1;
A_2=2;
L=1;

%Specify range of k values to plot on x axis
k=0:0.1:10;

%complex function to plot
t=(2*(A_1*A_2*cos(L*k) + A_1*A_2*sin(L*k)*1i))./(sin(L*k)*A_1^2*1i + 2*cos(L*k)*A_1*A_2 + sin(L*k)*A_2^2*1i);

%Finding magnitude of complex values
U=abs(t);

%Plot curve of U over specified range of k
plot(k,U);

disp("See that I added a dot just before the / sign!")

See that I added a dot just before the / sign!

Also, I made the increment of k smaller, for a smoother plot.

You might want to read this documentation about the difference between array and matrix operatoins.

[Kishan Rajah]

Thanks very much.

Answer 2

[Srinidhi]

A_1=1;
A_2=2;
L=1;
evec = [];
For k = [0:0.1:10]
t=(2*(A_1*A_2*cos(L*k) + A_1*A_2*sin(L*k)*1i))/(sin(L*k)*A_1^2*1i + 2*cos(L*k)*A_1*A_2 + sin(L*k)*A_2^2*1i);
F = abs(t);
evec = [evec F];
U = evec;
end
plot(k',U');

[Srinidhi]

Hope this helps.