151 lines
4.1 KiB
Fortran
151 lines
4.1 KiB
Fortran
SUBROUTINE SGETRSF( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO )
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*
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* -- LAPACK routine (version 3.0) --
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* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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* Courant Institute, Argonne National Lab, and Rice University
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* March 31, 1993
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*
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* .. Scalar Arguments ..
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CHARACTER TRANS
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INTEGER INFO, LDA, LDB, N, NRHS
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* ..
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* .. Array Arguments ..
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INTEGER IPIV( * )
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REAL A( LDA, * ), B( LDB, * )
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* ..
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*
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* Purpose
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* =======
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*
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* SGETRS solves a system of linear equations
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* A * X = B or A' * X = B
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* with a general N-by-N matrix A using the LU factorization computed
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* by SGETRF.
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*
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* Arguments
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* =========
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*
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* TRANS (input) CHARACTER*1
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* Specifies the form of the system of equations:
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* = 'N': A * X = B (No transpose)
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* = 'T': A'* X = B (Transpose)
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* = 'C': A'* X = B (Conjugate transpose = Transpose)
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*
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* N (input) INTEGER
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* The order of the matrix A. N >= 0.
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*
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* NRHS (input) INTEGER
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* The number of right hand sides, i.e., the number of columns
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* of the matrix B. NRHS >= 0.
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*
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* A (input) REAL array, dimension (LDA,N)
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* The factors L and U from the factorization A = P*L*U
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* as computed by SGETRF.
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*
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* LDA (input) INTEGER
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* The leading dimension of the array A. LDA >= max(1,N).
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*
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* IPIV (input) INTEGER array, dimension (N)
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* The pivot indices from SGETRF; for 1<=i<=N, row i of the
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* matrix was interchanged with row IPIV(i).
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*
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* B (input/output) REAL array, dimension (LDB,NRHS)
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* On entry, the right hand side matrix B.
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* On exit, the solution matrix X.
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*
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* LDB (input) INTEGER
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* The leading dimension of the array B. LDB >= max(1,N).
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*
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* INFO (output) INTEGER
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* = 0: successful exit
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* < 0: if INFO = -i, the i-th argument had an illegal value
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ONE
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PARAMETER ( ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL NOTRAN
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* ..
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* .. External Subroutines ..
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EXTERNAL SLASWP, STRSM, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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INFO = 0
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NOTRAN = LSAME( TRANS, 'N' )
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IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) .AND. .NOT.
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$ LSAME( TRANS, 'C' ) ) THEN
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INFO = -1
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ELSE IF( N.LT.0 ) THEN
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INFO = -2
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ELSE IF( NRHS.LT.0 ) THEN
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INFO = -3
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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -5
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ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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INFO = -8
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SGETRS', -INFO )
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RETURN
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END IF
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*
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* Quick return if possible
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*
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IF( N.EQ.0 .OR. NRHS.EQ.0 )
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$ RETURN
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*
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IF( NOTRAN ) THEN
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*
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* Solve A * X = B.
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*
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* Apply row interchanges to the right hand sides.
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*
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CALL SLASWP( NRHS, B, LDB, 1, N, IPIV, 1 )
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*
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* Solve L*X = B, overwriting B with X.
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*
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CALL STRSM( 'Left', 'Lower', 'No transpose', 'Unit', N, NRHS,
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$ ONE, A, LDA, B, LDB )
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*
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* Solve U*X = B, overwriting B with X.
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*
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CALL STRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N,
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$ NRHS, ONE, A, LDA, B, LDB )
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ELSE
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*
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* Solve A' * X = B.
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*
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* Solve U'*X = B, overwriting B with X.
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*
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CALL STRSM( 'Left', 'Upper', 'Transpose', 'Non-unit', N, NRHS,
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$ ONE, A, LDA, B, LDB )
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*
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* Solve L'*X = B, overwriting B with X.
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*
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CALL STRSM( 'Left', 'Lower', 'Transpose', 'Unit', N, NRHS, ONE,
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$ A, LDA, B, LDB )
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*
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* Apply row interchanges to the solution vectors.
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*
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CALL SLASWP( NRHS, B, LDB, 1, N, IPIV, -1 )
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END IF
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*
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RETURN
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*
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* End of SGETRS
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*
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END
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