Annotation of rpl/lapack/lapack/dtrtrs.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB,
! 2: $ INFO )
! 3: *
! 4: * -- LAPACK routine (version 3.2) --
! 5: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 6: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 7: * November 2006
! 8: *
! 9: * .. Scalar Arguments ..
! 10: CHARACTER DIAG, TRANS, UPLO
! 11: INTEGER INFO, LDA, LDB, N, NRHS
! 12: * ..
! 13: * .. Array Arguments ..
! 14: DOUBLE PRECISION A( LDA, * ), B( LDB, * )
! 15: * ..
! 16: *
! 17: * Purpose
! 18: * =======
! 19: *
! 20: * DTRTRS solves a triangular system of the form
! 21: *
! 22: * A * X = B or A**T * X = B,
! 23: *
! 24: * where A is a triangular matrix of order N, and B is an N-by-NRHS
! 25: * matrix. A check is made to verify that A is nonsingular.
! 26: *
! 27: * Arguments
! 28: * =========
! 29: *
! 30: * UPLO (input) CHARACTER*1
! 31: * = 'U': A is upper triangular;
! 32: * = 'L': A is lower triangular.
! 33: *
! 34: * TRANS (input) CHARACTER*1
! 35: * Specifies the form of the system of equations:
! 36: * = 'N': A * X = B (No transpose)
! 37: * = 'T': A**T * X = B (Transpose)
! 38: * = 'C': A**H * X = B (Conjugate transpose = Transpose)
! 39: *
! 40: * DIAG (input) CHARACTER*1
! 41: * = 'N': A is non-unit triangular;
! 42: * = 'U': A is unit triangular.
! 43: *
! 44: * N (input) INTEGER
! 45: * The order of the matrix A. N >= 0.
! 46: *
! 47: * NRHS (input) INTEGER
! 48: * The number of right hand sides, i.e., the number of columns
! 49: * of the matrix B. NRHS >= 0.
! 50: *
! 51: * A (input) DOUBLE PRECISION array, dimension (LDA,N)
! 52: * The triangular matrix A. If UPLO = 'U', the leading N-by-N
! 53: * upper triangular part of the array A contains the upper
! 54: * triangular matrix, and the strictly lower triangular part of
! 55: * A is not referenced. If UPLO = 'L', the leading N-by-N lower
! 56: * triangular part of the array A contains the lower triangular
! 57: * matrix, and the strictly upper triangular part of A is not
! 58: * referenced. If DIAG = 'U', the diagonal elements of A are
! 59: * also not referenced and are assumed to be 1.
! 60: *
! 61: * LDA (input) INTEGER
! 62: * The leading dimension of the array A. LDA >= max(1,N).
! 63: *
! 64: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
! 65: * On entry, the right hand side matrix B.
! 66: * On exit, if INFO = 0, the solution matrix X.
! 67: *
! 68: * LDB (input) INTEGER
! 69: * The leading dimension of the array B. LDB >= max(1,N).
! 70: *
! 71: * INFO (output) INTEGER
! 72: * = 0: successful exit
! 73: * < 0: if INFO = -i, the i-th argument had an illegal value
! 74: * > 0: if INFO = i, the i-th diagonal element of A is zero,
! 75: * indicating that the matrix is singular and the solutions
! 76: * X have not been computed.
! 77: *
! 78: * =====================================================================
! 79: *
! 80: * .. Parameters ..
! 81: DOUBLE PRECISION ZERO, ONE
! 82: PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
! 83: * ..
! 84: * .. Local Scalars ..
! 85: LOGICAL NOUNIT
! 86: * ..
! 87: * .. External Functions ..
! 88: LOGICAL LSAME
! 89: EXTERNAL LSAME
! 90: * ..
! 91: * .. External Subroutines ..
! 92: EXTERNAL DTRSM, XERBLA
! 93: * ..
! 94: * .. Intrinsic Functions ..
! 95: INTRINSIC MAX
! 96: * ..
! 97: * .. Executable Statements ..
! 98: *
! 99: * Test the input parameters.
! 100: *
! 101: INFO = 0
! 102: NOUNIT = LSAME( DIAG, 'N' )
! 103: IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 104: INFO = -1
! 105: ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
! 106: $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
! 107: INFO = -2
! 108: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
! 109: INFO = -3
! 110: ELSE IF( N.LT.0 ) THEN
! 111: INFO = -4
! 112: ELSE IF( NRHS.LT.0 ) THEN
! 113: INFO = -5
! 114: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
! 115: INFO = -7
! 116: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
! 117: INFO = -9
! 118: END IF
! 119: IF( INFO.NE.0 ) THEN
! 120: CALL XERBLA( 'DTRTRS', -INFO )
! 121: RETURN
! 122: END IF
! 123: *
! 124: * Quick return if possible
! 125: *
! 126: IF( N.EQ.0 )
! 127: $ RETURN
! 128: *
! 129: * Check for singularity.
! 130: *
! 131: IF( NOUNIT ) THEN
! 132: DO 10 INFO = 1, N
! 133: IF( A( INFO, INFO ).EQ.ZERO )
! 134: $ RETURN
! 135: 10 CONTINUE
! 136: END IF
! 137: INFO = 0
! 138: *
! 139: * Solve A * x = b or A' * x = b.
! 140: *
! 141: CALL DTRSM( 'Left', UPLO, TRANS, DIAG, N, NRHS, ONE, A, LDA, B,
! 142: $ LDB )
! 143: *
! 144: RETURN
! 145: *
! 146: * End of DTRTRS
! 147: *
! 148: END
CVSweb interface <joel.bertrand@systella.fr>