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# MatMFFDCheckPositivity

Checks that all entries in \(U + h*a \) are positive or zero, decreases `h` until this is satisfied for a `MATMFFD` matrix

## Synopsis

    #include "petscmat.h"
    PetscErrorCode MatMFFDCheckPositivity(void *dummy, Vec U, Vec a, PetscScalar *h)

Logically Collective

## Input Parameters

- dummy - context variable (unused)

- U - base vector that is added to

- a - vector that is added

- h - scaling factor on `a`, may be changed on output

## Options Database Keys

- -mat_mffd_check_positivity <bool> - Ensure that \(U + h*a\) is nonnegative

## Note

This is rarely used directly, rather it is passed as an argument to `MatMFFDSetCheckh()`

## See Also

Matrices, `Mat`, `MATMFFD`, `MatMFFDSetCheckh()`

## Level

advanced

## Location

src/mat/impls/mffd/mffd.c

Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages