MATLAB Function Reference

spfun

Apply function to nonzero sparse matrix elements

Syntax

• f = spfun(fun,S)
  

Description

The spfun function selectively applies a function to only the nonzero elements of a sparse matrix S, preserving the sparsity pattern of the original matrix (except for underflow or if fun returns zero for some nonzero elements of S).

f = spfun(fun,S) evaluates fun(S) on the nonzero elements of S. You can specify fun as a function handle or as an inline object.

Remarks

Functions that operate element-by-element, like those in the elfun directory, are the most appropriate functions to use with spfun.

Examples

Given the 4-by-4 sparse diagonal matrix

• S = spdiags([1:4]',0,4,4)
  
  S = 
     (1,1)        1
     (2,2)        2
     (3,3)        3
     (4,4)        4
  

Because fun returns nonzero values for all nonzero element of S, f = spfun(@exp,S) has the same sparsity pattern as S.

• f =
     (1,1)       2.7183
     (2,2)       7.3891
     (3,3)      20.0855
     (4,4)      54.5982
  

whereas exp(S) has 1s where S has 0s.

• full(exp(S))
  
  ans =
      2.7183    1.0000    1.0000    1.0000
      1.0000    7.3891    1.0000    1.0000
      1.0000    1.0000   20.0855    1.0000
      1.0000    1.0000    1.0000   54.5982
  

See Also

function handle (@), inline

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