The stem plots are intended to depict discrete data, specifically relating to signal processing, not the continuous data of other plots. If you have a matrix, use surf or mesh or related functions.
You can use stem3 with matrix arguments if you convert them into vectors first. For example if ‘X’, ‘Y’ and ‘Z’ are equal-sized matrices, you can convert them to vectors and plot them as:
figure(1)
stem3(X(:), Y(:), Z(:))
grid on
