Campus Livre
spy
Visualizes the sparsity pattern of a matrix.
Category: Mathematics > Sparse Matrices
Syntax
spy(S)Plots a dot for every nonzero element of S.
spy(S, LineSpec)Uses a color and marker given by LineSpec.
Description
The plot has the matrix layout, with row 1 at the top, and shows the number of nonzeros under the axis. It quickly reveals structure: bands, blocks, arrow shapes, and the effect of a reordering such as symrcm on the fill pattern.
Input arguments
S- Sparse or full matrix.
LineSpec- Optional marker specification such as
'r*'.
Example
Pattern of a banded matrix
e = ones(12, 1);
A = spdiags([e e e e e], -2:2, 12, 12);
spy(A)