spy

Purpose

Visualize matrix sparsity patterns.

spy(S)
spy(S,marksize)
spy(S,'color')
spy(S,'color',marksize)

spy(S) plots the sparsity pattern of any matrix S.

spy(S,marksize), where marksize is an integer, uses the specified marker size.

spy(S,'color'), where color is a string, uses the specified color for the plot markers.

spy(S,'color',marksize) uses the specified color and size for the plot markers.

S is usually a sparse matrix, but full matrices are acceptable, in which case the locations of the nonzero elements are plotted.

spy replaces format +, which takes much more space to display essentially the same information.