Phase portrait for a matrix

I have solved a system of ODEs, and would like to plot a phase portrait in MATLAB. This gave me the following matrix:

[ 1, i ; 3, 5i]

How can I simply plot the spiral potrait in MATLAB for this?

Thanks

[Birdman]

Can you share your differential equations?

Answer 1

[Sergio Manzetti]

Yes, it is:

5i Y'' - 3i Y' = 0