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SUBROUTINE FBSINV (X,Y,IOBUFF)
C
C SINGLE PRECISION VERSION
C
C FBSINV IS A SPECIAL FORWARD-BACKWARD SUBSTITUTION ROUTINE FOR
C INVPWR. IT OPERATES ON CONJUNCTION WITH SDCOMP.
C THE ARITHMETIC PRECISION IS THAT OF THE INPUT FILE
C
C FILEL = MATRIX CONTROL BLOCK FOR THE LOWER TRIANGLE
C X = THE LOAD VECTOR
C Y = THE SOLUTION VECTOR
C IOBUFF = NOT USED
C
INTEGER FILEL ,PARM(3) ,IBLK(15)
REAL X(1) ,Y(1)
COMMON /FBSX / FILEL(7)
EQUIVALENCE (FILEL(3),NROW), (FILEL(5),LTYPE)
DATA PARM / 4H ,4HFBSI, 4HNV /
C
C FORWARD PASS
C
PARM(1) = FILEL(1)
IBLK(1) = FILEL(1)
IF (LTYPE .EQ. 2) GO TO 20
IF (LTYPE .NE. 1) GO TO 50
C
C TRANSFER THE SINGLE PRECISION LOAD VECTOR TO THE SOLUTION VECTOR
C
DO 10 I = 1,NROW
10 Y(I) = X(I)
CALL FBS1 (IBLK,Y,Y,NROW)
GO TO 40
C
C TRANSFER THE DOUBLE PRECISION LOAD VECTOR TO THE SOLUTION VECTOR
C
20 NROW2 = 2*NROW
DO 30 I = 1,NROW2
30 Y(I) = X(I)
CALL FBS2 (IBLK,Y,Y,NROW2)
C
40 CALL REWIND (FILEL)
CALL SKPREC (FILEL,1)
RETURN
C
C FATAL ERRORS
C
50 CALL MESAGE (-7,PARM(1),PARM(2))
RETURN
END
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