# STSetMatStructure

Sets an internal MatStructure attribute to indicate which is the relation of the sparsity pattern of the two matrices A and B constituting the generalized eigenvalue problem.

### Synopsis

    #include "slepcst.h"
    PetscErrorCode STSetMatStructure(ST st,MatStructure str)

Logically Collective on ST

### Input Parameters

| st | - the spectral transformation context
| str | - either SAME_NONZERO_PATTERN, DIFFERENT_NONZERO_PATTERN or SUBSET_NONZERO_PATTERN

### Options Database Key

-st_matstructure <str> - Indicates the structure flag, where <str> is one of 'same' (A and B have the same nonzero pattern), 'different' (A and B have different nonzero pattern) or 'subset' (B's nonzero pattern is a subset of A's).

### Notes

By default, the sparsity patterns are assumed to be different. If the patterns are equal or a subset then it is recommended to set this attribute for efficiency reasons (in particular, for internal MatAXPY() operations).

This function has no effect in the case of standard eigenproblems.

### See Also

STSetOperators(), MatAXPY()

Location: src/st/interface/stset.c
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