# NAG Library Routine Document

## 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 nagmk26.h
 void d02nrf_ (Integer *j, Integer *iplace, const Integer inform[])

## 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 (a argument of d02nmf or d02nnf).
See the D02M–N Sub-chapter Introduction.

## 5Arguments

1:     $\mathbf{j}$ – IntegerOutput
On exit: the index $j$ of the column of the Jacobian which is required.
2:     $\mathbf{iplace}$ – IntegerOutput
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 arrayCommunication Array
On entry: contains information supplied by the integrator.

None.

Not applicable.

## 8Parallelism and Performance

d02nrf is not threaded in any implementation.