spy

Visualize sparsity pattern of matrix

• 

Syntax

spy(S)

spy(S,LineSpec)

spy(___,MarkerSize)

Description

spy(S) plots the sparsity pattern of matrix S. Nonzero values are colored while zero values are white. The plot displays the number of nonzeros in the matrix, nz = nnz(S).

spy(S,LineSpec) additionally specifies LineSpec to give the marker symbol and color to use in the plot. For example, spy(A,'r*') uses red asterisks for nonzeros.

spy(___,MarkerSize) specifies MarkerSize to give the size of the markers using either of the previous input argument combinations.

Examples

Plot Sparsity Pattern

Plot the 60-by-60 sparse adjacency matrix of the connectivity graph of the Buckminster Fuller geodesic dome. This matrix also represents the carbon-60 molecule and a soccer ball.

B = bucky;
spy(B)

Specify the color and marker.

spy(B,'ro')

Also specify the marker size.

spy(B,'ro',2)

Input Arguments

S — Input matrix

matrix

Input matrix. S is typically a sparse matrix, but can be either full or sparse.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical
Complex Number Support: Yes

MarkerSize — Size of markers

positive integer scalar

Size of markers, specified as a positive integer scalar.

Example: spy(A,3) uses markers of size 3.

LineSpec — Marker symbol and color

character vector | string

Marker symbol and color, specified as a character vector or string containing symbols. The symbols can appear in any order. You do not need to specify both characteristics (marker and color). For example, if you omit the color and specify the marker, then the plot uses the default colors but uses the specified markers.

Example: 'or' uses red circle markers.

Marker	Description	Resulting Marker
"o"	Circle
"+"	Plus sign
"*"	Asterisk
"."	Point
"x"	Cross
"_"	Horizontal line
"|"	Vertical line
"square"	Square
"diamond"	Diamond
"^"	Upward-pointing triangle
"v"	Downward-pointing triangle
">"	Right-pointing triangle
"<"	Left-pointing triangle
"pentagram"	Pentagram
"hexagram"	Hexagram

Color Name	Short Name	Appearance
'red'	'r'
'green'	'g'
'blue'	'b'
'cyan'	'c'
'magenta'	'm'
'yellow'	'y'
'black'	'k'
'white'	'w'

Tips

• format + is a text-based alternative for displaying the nonzero structure of a small matrix:

  format +
  eye(4)

  ans =
  
  +   
   +  
    + 
     +

Extended Capabilities

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The spy function supports GPU array input with these usage notes and limitations:

• This function accepts GPU arrays, but does not run on a GPU.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Distributed Arrays

Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

Usage notes and limitations:

• This function operates on distributed arrays, but executes in the client MATLAB^®.

For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Version History

Introduced before R2006a

R2023a: Aspect ratio and marker size changes

The aspect ratio of spy plots has a 1-to-10 limit, after which the plot stops adjusting to the matrix shape. You can use pbaspect("auto") for no special aspect ratio or pbaspect([size(A,2) size(A,1) 1]) for the previous behavior of a matching aspect ratio, even for very "squeezed" cases.

Additionally, the default marker size is based only on the matrix size. Previously, the point size of the axes on creation could also affect the marker size.