# NAG FL Interfaced02nrf (ivp_​stiff_​sparjac_​enq)

## 1Purpose

d02nrf is an enquiry routine for communicating with d02nmf or d02nnf when supplying columns of a sparse Jacobian matrix.

## 2Specification

Fortran Interface
 Subroutine d02nrf ( j,
 Integer, Intent (In) :: inform(23) Integer, Intent (Out) :: j, iplace
#include <nag.h>
 void d02nrf_ (Integer *j, Integer *iplace, const Integer inform[])
The routine may be called by the names d02nrf or nagf_ode_ivp_stiff_sparjac_enq.

## 3Description

d02nrf is required when d02nmf or d02nnf is being used with sparse matrix linear algebra. After an exit from d02nmf or d02nnf with ${\mathbf{irevcm}}=8$, d02nrf must be called to determine which column of the Jacobian is required and where it is to be placed in the array rwork (an argument of d02nmf or d02nnf).

## 4References

See the D02MN Sub-chapter Introduction.

## 5Arguments

1: $\mathbf{j}$Integer Output
On exit: the index $j$ of the column of the Jacobian which is required.
2: $\mathbf{iplace}$Integer Output
On exit: indicates which locations in the array rwork to fill with the $j$th column.
If ${\mathbf{iplace}}=1$, the $\left(i,j\right)$th element of the Jacobian must be placed in ${\mathbf{rwork}}\left(50+2×{\mathbf{ldysav}}+i\right)$, otherwise the $\left(i,j\right)$th element must be placed in ${\mathbf{rwork}}\left(50+{\mathbf{ldysav}}+i\right)$.
If ${\mathbf{jceval}}=\text{'F'}$, in the previous call to d02nuf, ${\mathbf{iplace}}=2$ always, hence the $j$th column of the Jacobian must be placed in ${\mathbf{rwork}}\left(50+{\mathbf{ldysav}}+\mathit{i}\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{neq}}$.
rwork, neq and ldysav are arguments of d02nmf and d02nnf.
3: $\mathbf{inform}\left(23\right)$Integer array Communication Array
On entry: contains information supplied by the integrator.

None.

Not applicable.

## 8Parallelism and Performance

d02nrf is not threaded in any implementation.