# PetscDSGetBdJacobian
Get the pointwise boundary Jacobian function for given test and basis field 
## Synopsis
```
#include "petscds.h" 
PetscErrorCode PetscDSGetBdJacobian(PetscDS ds, PetscInt f, PetscInt g, void (**g0)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], const PetscReal n[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g0[]), void (**g1)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], const PetscReal n[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g1[]), void (**g2)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], const PetscReal n[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g2[]), void (**g3)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, PetscReal u_tShift, const PetscReal x[], const PetscReal n[], PetscInt numConstants, const PetscScalar constants[], PetscScalar g3[]))
```
Not collective


## Input Parameters

- ***ds -*** The `PetscDS`
- ***f  -*** The test field number
- ***g  -*** The field number



## Output Parameters

- ***g0 -*** integrand for the test and basis function term
- ***g1 -*** integrand for the test function and basis function gradient term
- ***g2 -*** integrand for the test function gradient and basis function term
- ***g3 -*** integrand for the test function gradient and basis function gradient term



## Calling sequence for the callbacks g0, g1, g2 and g3
```none
  g0(PetscInt dim, PetscInt Nf, PetscInt NfAux,
     const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[],
     const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[],
     PetscReal t, const PetscReal x[], const PetscReal n[], PetscScalar g0[])
```


- ***dim -*** the spatial dimension
- ***Nf -*** the number of fields
- ***uOff -*** the offset into u[] and u_t[] for each field
- ***uOff_x -*** the offset into u_x[] for each field
- ***u -*** each field evaluated at the current point
- ***u_t -*** the time derivative of each field evaluated at the current point
- ***u_x -*** the gradient of each field evaluated at the current point
- ***aOff -*** the offset into a[] and a_t[] for each auxiliary field
- ***aOff_x -*** the offset into a_x[] for each auxiliary field
- ***a -*** each auxiliary field evaluated at the current point
- ***a_t -*** the time derivative of each auxiliary field evaluated at the current point
- ***a_x -*** the gradient of auxiliary each field evaluated at the current point
- ***t -*** current time
- ***u_tShift -*** the multiplier a for dF/dU_t
- ***x -*** coordinates of the current point
- ***n -*** normal at the current point
- ***numConstants -*** number of constant parameters
- ***constants -*** constant parameters
- ***g0 -*** output values at the current point





## Note

## We are using a first order FEM model for the weak form
\int_\Gamma \phi {\vec g}_0(u, u_t, \nabla u, x, t) \cdot \hat n \psi + \phi {\vec g}_1(u, u_t, \nabla u, x, t) \cdot \hat n \nabla \psi + \nabla\phi \cdot {\vec g}_2(u, u_t, \nabla u, x, t) \cdot \hat n \psi + \nabla\phi \cdot {\overleftrightarrow g}_3(u, u_t, \nabla u, x, t) \cdot \hat n \cdot \nabla \psi


## See Also
 `PetscDS`, `PetscDSSetBdJacobian()`

## Level
intermediate

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


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