PCHNGS(3)

SYNOPSIS
SUBROUTINE PCHNGS (II, XVAL, IPLACE, SX, IX, IRCX)

NAME
pchngs - Subsidiary to SPLP

LIBRARY
SLATEC

TYPE
SINGLE PRECISION (PCHNGS-S, DPCHNG-D)

AUTHOR
Hanson, R. J., (SNLA) Wisniewski, J. A., (SNLA)

DESCRIPTION
PCHNGS LIMITS THE TYPE OF STORAGE TO A SEQUENTIAL SCHEME. SPARSE MATRIX ELEMENT ALTERATION SUBROUTINE. SUBROUTINE PCHNGS() CHANGES ELEMENT II IN VECTOR +/- IRCX TO THE VALUE XVAL. II THE ABSOLUTE VALUE OF THIS INTEGER IS THE SUBSCRIPT FOR THE ELEMENT TO BE CHANGED. XVAL NEW VALUE OF THE MATRIX ELEMENT BEING CHANGED. IPLACE POINTER INFORMATION WHICH IS MAINTAINED BY THE PACKAGE. SX(*),IX(*) THE WORK ARRAYS WHICH ARE USED TO STORE THE SPARSE MATRIX. THESE ARRAYS ARE AUTOMATICALLY MAINTAINED BY THE PACKAGE FOR THE USER. IRCX POINTS TO THE VECTOR OF THE MATRIX BEING UPDATED. A NEGATIVE VALUE OF IRCX INDICATES THAT ROW -IRCX IS BEING UPDATED. A POSITIVE VALUE OF IRCX INDICATES THAT COLUMN IRCX IS BEING UPDATED. A ZERO VALUE OF IRCX IS AN ERROR. SINCE DATA ITEMS ARE KEPT SORTED IN THE SEQUENTIAL DATA STRUCTURE, CHANGING A MATRIX ELEMENT CAN REQUIRE THE MOVEMENT OF ALL THE DATA ITEMS IN THE MATRIX. FOR THIS REASON, IT IS SUGGESTED THAT DATA ITEMS BE ADDED A COL. AT A TIME, IN ASCENDING COL. SEQUENCE. FURTHERMORE, SINCE DELETING ITEMS FROM THE DATA STRUCTURE MAY ALSO REQUIRE MOVING LARGE AMOUNTS OF DATA, ZERO ELEMENTS ARE EXPLICITLY STORED IN THE MATRIX. THIS SUBROUTINE IS A MODIFICATION OF THE SUBROUTINE LCHNGS, SANDIA LABS. REPT. SAND78-0785. MODIFICATIONS BY K.L. HIEBERT AND R.J. HANSON

REVISED 811130-1000 REVISED YYMMDD-HHMM

SEE ALSO
SPLP

ROUTINES CALLED
IPLOC, PRWPGE, XERMSG

REVISION HISTORY (YYMMDD)
811215 DATE WRITTEN
890531 Changed all specific intrinsics to generic. (WRB)
891214 Prologue converted to Version 4.0 format. (BAB)
900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
900328 Added TYPE section. (WRB)
910403 Updated AUTHOR and DESCRIPTION sections. (WRB)