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Diffstat (limited to 'SRC/stbtrs.f')
| -rw-r--r-- | SRC/stbtrs.f | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/SRC/stbtrs.f b/SRC/stbtrs.f new file mode 100644 index 00000000..39e47d62 --- /dev/null +++ b/SRC/stbtrs.f @@ -0,0 +1,162 @@ + SUBROUTINE STBTRS( UPLO, TRANS, DIAG, N, KD, NRHS, AB, LDAB, B, + $ LDB, INFO ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER DIAG, TRANS, UPLO + INTEGER INFO, KD, LDAB, LDB, N, NRHS +* .. +* .. Array Arguments .. + REAL AB( LDAB, * ), B( LDB, * ) +* .. +* +* Purpose +* ======= +* +* STBTRS solves a triangular system of the form +* +* A * X = B or A**T * X = B, +* +* where A is a triangular band matrix of order N, and B is an +* N-by NRHS matrix. A check is made to verify that A is nonsingular. +* +* Arguments +* ========= +* +* UPLO (input) CHARACTER*1 +* = 'U': A is upper triangular; +* = 'L': A is lower triangular. +* +* TRANS (input) CHARACTER*1 +* Specifies the form the system of equations: +* = 'N': A * X = B (No transpose) +* = 'T': A**T * X = B (Transpose) +* = 'C': A**H * X = B (Conjugate transpose = Transpose) +* +* DIAG (input) CHARACTER*1 +* = 'N': A is non-unit triangular; +* = 'U': A is unit triangular. +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* KD (input) INTEGER +* The number of superdiagonals or subdiagonals of the +* triangular band matrix A. KD >= 0. +* +* NRHS (input) INTEGER +* The number of right hand sides, i.e., the number of columns +* of the matrix B. NRHS >= 0. +* +* AB (input) REAL array, dimension (LDAB,N) +* The upper or lower triangular band matrix A, stored in the +* first kd+1 rows of AB. The j-th column of A is stored +* in the j-th column of the array AB as follows: +* if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; +* if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd). +* If DIAG = 'U', the diagonal elements of A are not referenced +* and are assumed to be 1. +* +* LDAB (input) INTEGER +* The leading dimension of the array AB. LDAB >= KD+1. +* +* B (input/output) REAL array, dimension (LDB,NRHS) +* On entry, the right hand side matrix B. +* On exit, if INFO = 0, the solution matrix X. +* +* LDB (input) INTEGER +* The leading dimension of the array B. LDB >= max(1,N). +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -i, the i-th argument had an illegal value +* > 0: if INFO = i, the i-th diagonal element of A is zero, +* indicating that the matrix is singular and the +* solutions X have not been computed. +* +* ===================================================================== +* +* .. Parameters .. + REAL ZERO + PARAMETER ( ZERO = 0.0E+0 ) +* .. +* .. Local Scalars .. + LOGICAL NOUNIT, UPPER + INTEGER J +* .. +* .. External Functions .. + LOGICAL LSAME + EXTERNAL LSAME +* .. +* .. External Subroutines .. + EXTERNAL STBSV, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + INFO = 0 + NOUNIT = LSAME( DIAG, 'N' ) + UPPER = LSAME( UPLO, 'U' ) + IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN + INFO = -1 + ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT. + $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN + INFO = -2 + ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN + INFO = -3 + ELSE IF( N.LT.0 ) THEN + INFO = -4 + ELSE IF( KD.LT.0 ) THEN + INFO = -5 + ELSE IF( NRHS.LT.0 ) THEN + INFO = -6 + ELSE IF( LDAB.LT.KD+1 ) THEN + INFO = -8 + ELSE IF( LDB.LT.MAX( 1, N ) ) THEN + INFO = -10 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'STBTRS', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) + $ RETURN +* +* Check for singularity. +* + IF( NOUNIT ) THEN + IF( UPPER ) THEN + DO 10 INFO = 1, N + IF( AB( KD+1, INFO ).EQ.ZERO ) + $ RETURN + 10 CONTINUE + ELSE + DO 20 INFO = 1, N + IF( AB( 1, INFO ).EQ.ZERO ) + $ RETURN + 20 CONTINUE + END IF + END IF + INFO = 0 +* +* Solve A * X = B or A' * X = B. +* + DO 30 J = 1, NRHS + CALL STBSV( UPLO, TRANS, DIAG, N, KD, AB, LDAB, B( 1, J ), 1 ) + 30 CONTINUE +* + RETURN +* +* End of STBTRS +* + END |