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*DECK MSRILU
SUBROUTINE MSRILU(N,LC,IM,MCU,JU,DIAGF,CF)
*
*-----------------------------------------------------------------------
*
*Purpose:
* In-place ILU0 decomposition of a matrix store in MSR format.
* The resulting matrix is in "L\U-I" format with inversed diagonal elements
* It is assumed that each line of the matrix is sorted by increasing
* column index.
*
*Reference
* Y. Saad, "Iterative Methods for Sparse Linear Systems",
* PWS Publishing Company, Boston, 1996
*
*Copyright:
* Copyright (C) 2002 Ecole Polytechnique de Montreal
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version
*
*Author(s): R. Le Tellier
*
*Parameters: input
* N size of the matrix.
* LC dimension of IM.
* IM elements of row i in MCU(IM(i):IM(i+1)-1)
* MCU
* JU MCU(JU(i):IM(i+1)) corresponds to U.
* MCU(IM(i)+1:JU(i)-1) correspond to L.
*
* Parameters: input/output
* DIAGF diagonal elements of the matrix to process / U (inversed diagonal).
* CF non-diagonal elements of the matrix to process / L and U.
*
*-----------------------------------------------------------------------
*
IMPLICIT NONE
*---
* SUBROUTINE ARGUMENTS
*---
INTEGER N,LC,IM(N+1),MCU(LC),JU(N)
DOUBLE PRECISION DIAGF(N),CF(LC)
*---
* LOCAL VARIABLES
*---
DOUBLE PRECISION EPS
PARAMETER(EPS=1D-7)
INTEGER I,K,J,H,IK,IJ,KJ,IH
DOUBLE PRECISION E
INTEGER, ALLOCATABLE, DIMENSION(:) :: IW
*----
* SCRATCH STORAGE ALLOCATION
*----
ALLOCATE(IW(N))
*
IW(:N)=0
*---
* LOOP OVER LINE INDEX I
*---
DO I=1,N
* store component H in relation with I
DO IH=IM(I)+1,IM(I+1)
H=MCU(IH)
IF (H.GT.0) IW(H)=IH
ENDDO
* ---
* LOOP OVER LINE K < I IN RELATION WITH I
* ---
DO IK=IM(I)+1,JU(I)-1
K=MCU(IK)
IF (K.GT.0) THEN
* entry (I>K,K)
E=DIAGF(K)*CF(IK)
CF(IK)=E
* ---
* LOOP OVER COLUMN J > K IN RELATION WITH K
* ---
DO KJ=JU(K),IM(K+1)
J=MCU(KJ)
* entry (I>K,J>K)
IF (I.EQ.J) THEN ! diagonal term
DIAGF(J)=DIAGF(J)-E*CF(KJ)
ELSEIF(IW(J).GT.0) THEN ! if J is in relation with I
IJ=IW(J)
CF(IJ)=CF(IJ)-E*CF(KJ)
ENDIF
ENDDO
ENDIF
ENDDO
IF (ABS(DIAGF(I)).GT.EPS) THEN
DIAGF(I)=1.0/DIAGF(I)
ELSE
WRITE(6,*) 'I=',I,' PIVOT=',DIAGF(I)
CALL PRINDM('DIAGF ',DIAGF,N)
CALL PRINDM('CF ',CF,LC)
CALL XABORT('MSRILU: ZERO PIVOT')
ENDIF
* reset IW
DO IH=IM(I)+1,IM(I+1)
H=MCU(IH)
IF (H.GT.0) THEN
IW(H)=0
ENDIF
ENDDO
ENDDO
*----
* SCRATCH STORAGE DEALLOCATION
*----
DEALLOCATE(IW)
RETURN
END
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