D02 Chapter Contents
D02 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentD02NRF

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

## 1  Purpose

D02NRF is an enquiry routine for communicating with D02NMF or D02NNF when supplying columns of a sparse Jacobian matrix.

## 2  Specification

 SUBROUTINE D02NRF ( J, IPLACE, INFORM)
 INTEGER J, IPLACE, INFORM(23)

## 3  Description

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 parameter of D02NMF or D02NNF).
See the D02M–N sub-chapter Introduction.

## 5  Parameters

1:     J – INTEGEROutput
On exit: the index $j$ of the column of the Jacobian which is required.
2:     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, then ${\mathbf{IPLACE}}=2$ 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 parameters of D02NMF and D02NNF.
3:     INFORM($23$) – INTEGER arrayCommunication Array
On entry: contains information supplied by the integrator.

None.

Not applicable.