Create a legend for complex numbers plot

Hi,

I am plotting m by n matrices of complex numbers using

figure;
plot(poles_sys_a, 'kx'); hold on;
plot(poles_sys_b, 'ro'); hold off;  

How can I insert a legend into that plot, that correctly labels the two sets?

legend('poles of sys_a','poles of sys_b');

doesn't work.

For example try

poles_sys_a = rand(3,10) + i*rand(3,10);
poles_sys_b = rand(3,1) + i*rand(3,1);

Thanks a lot.

JJ

Answer 1

[Star Strider]

Your ‘poles_sys_a’ matrix is confusing the plot function. If you create the ‘poles_sys_a’ matrix to vectors (using the ‘(:)’ notation), it works correctly with the legend call:

poles_sys_a = rand(3,4) + 1i*rand(3,4);
poles_sys_b = rand(3,1) + 1i*rand(3,1);

figure;
ha = plot(real(poles_sys_a(:)), imag(poles_sys_a(:)), 'kx');
hold on
hb = plot(real(poles_sys_b), imag(poles_sys_b), 'rx');
hold off  
legend('poles of sys_a','poles of sys_b');

I decreased the size of ‘poles_sys_a’ so I could be certain it plots correctly with my changes. (It does.) I also changed the red 'o' to 'x' because by convention ‘x’ indicate pole locations, and ‘o’ zero locations.

[JJ]

That worked. Thank you very much.

[Star Strider]

As always, my pleasure.

Answer 2

[madhan ravi]

legend({'poles of sys_a','poles of sys_b'})

[JJ]

Nope, doesn't work. It still displays a black cross where a red circle should appear in the legend.

[madhan ravi]

provide your datas to test

[Walter Roberson]

When I try in R2018b, I get a legend with black x and red o

[JJ]

I'm using R2018b. But just black crosses.

[madhan ravi]

Even am using 2018b I get the same result as sir Walter

[JJ]

I added the example, so the question is still open.