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# PetscDTBaryToIndex
convert a barycentric coordinate to an index 
## Synopsis
```
#include "petscdt.h" 
PetscErrorCode PetscDTBaryToIndex(PetscInt len, PetscInt sum, const PetscInt coord[], PetscInt *index)
```

## Input Parameters

- ***len -*** the desired length of the barycentric tuple (usually 1 more than the dimension it represents, so a barycentric coordinate in a triangle has length 3)
- ***sum -*** the value that the sum of the barycentric coordinates (which will be non-negative integers) should sum to
- ***coord -*** a barycentric coordinate with the given length and sum



## Output Parameter

- ***index -*** the unique index for the coordinate, >= 0 and < Binomial(len - 1 + sum, sum)





## Note
The indices map to barycentric coordinates in lexicographic order, where the first index is the
least significant and the last index is the most significant.


## See Also
 `PetscDTIndexToBary`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/dt/interface/dt.c.html#PetscDTBaryToIndex">src/dm/dt/interface/dt.c</A>


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[Index of all DT routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)