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# PetscIsNanReal
Returns whether the `PetscReal` input is a Not-a-Number (NaN) value. 
## Synopsis
```
#if defined(PETSC_USE_REAL___FLOAT128)
PetscBool PetscIsNanReal(PetscReal a)
```

## Input Parameter

- ***a -*** the floating point number





## Developer Notes
Uses the C99 standard `isnan()` on systems where it exists.

Otherwise uses (a != a), note that some optimizing compilers compile
out this form, thus removing the check.


## See Also
 `PetscIsNormalReal()`, `PetscIsInfReal()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/sys/utils/mathinf.c.html#PetscIsNanReal">src/sys/utils/mathinf.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/sys/utils/mathinf.c)


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