Annotation of rpl/lapack/lapack/dtptrs.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
! 2: *
! 3: * -- LAPACK routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: CHARACTER DIAG, TRANS, UPLO
! 10: INTEGER INFO, LDB, N, NRHS
! 11: * ..
! 12: * .. Array Arguments ..
! 13: DOUBLE PRECISION AP( * ), B( LDB, * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * DTPTRS solves a triangular system of the form
! 20: *
! 21: * A * X = B or A**T * X = B,
! 22: *
! 23: * where A is a triangular matrix of order N stored in packed format,
! 24: * and B is an N-by-NRHS matrix. A check is made to verify that A is
! 25: * 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: * AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
! 52: * The upper or lower triangular matrix A, packed columnwise in
! 53: * a linear array. The j-th column of A is stored in the array
! 54: * AP as follows:
! 55: * if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
! 56: * if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
! 57: *
! 58: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
! 59: * On entry, the right hand side matrix B.
! 60: * On exit, if INFO = 0, the solution matrix X.
! 61: *
! 62: * LDB (input) INTEGER
! 63: * The leading dimension of the array B. LDB >= max(1,N).
! 64: *
! 65: * INFO (output) INTEGER
! 66: * = 0: successful exit
! 67: * < 0: if INFO = -i, the i-th argument had an illegal value
! 68: * > 0: if INFO = i, the i-th diagonal element of A is zero,
! 69: * indicating that the matrix is singular and the
! 70: * solutions X have not been computed.
! 71: *
! 72: * =====================================================================
! 73: *
! 74: * .. Parameters ..
! 75: DOUBLE PRECISION ZERO
! 76: PARAMETER ( ZERO = 0.0D+0 )
! 77: * ..
! 78: * .. Local Scalars ..
! 79: LOGICAL NOUNIT, UPPER
! 80: INTEGER J, JC
! 81: * ..
! 82: * .. External Functions ..
! 83: LOGICAL LSAME
! 84: EXTERNAL LSAME
! 85: * ..
! 86: * .. External Subroutines ..
! 87: EXTERNAL DTPSV, XERBLA
! 88: * ..
! 89: * .. Intrinsic Functions ..
! 90: INTRINSIC MAX
! 91: * ..
! 92: * .. Executable Statements ..
! 93: *
! 94: * Test the input parameters.
! 95: *
! 96: INFO = 0
! 97: UPPER = LSAME( UPLO, 'U' )
! 98: NOUNIT = LSAME( DIAG, 'N' )
! 99: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 100: INFO = -1
! 101: ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
! 102: $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
! 103: INFO = -2
! 104: ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
! 105: INFO = -3
! 106: ELSE IF( N.LT.0 ) THEN
! 107: INFO = -4
! 108: ELSE IF( NRHS.LT.0 ) THEN
! 109: INFO = -5
! 110: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
! 111: INFO = -8
! 112: END IF
! 113: IF( INFO.NE.0 ) THEN
! 114: CALL XERBLA( 'DTPTRS', -INFO )
! 115: RETURN
! 116: END IF
! 117: *
! 118: * Quick return if possible
! 119: *
! 120: IF( N.EQ.0 )
! 121: $ RETURN
! 122: *
! 123: * Check for singularity.
! 124: *
! 125: IF( NOUNIT ) THEN
! 126: IF( UPPER ) THEN
! 127: JC = 1
! 128: DO 10 INFO = 1, N
! 129: IF( AP( JC+INFO-1 ).EQ.ZERO )
! 130: $ RETURN
! 131: JC = JC + INFO
! 132: 10 CONTINUE
! 133: ELSE
! 134: JC = 1
! 135: DO 20 INFO = 1, N
! 136: IF( AP( JC ).EQ.ZERO )
! 137: $ RETURN
! 138: JC = JC + N - INFO + 1
! 139: 20 CONTINUE
! 140: END IF
! 141: END IF
! 142: INFO = 0
! 143: *
! 144: * Solve A * x = b or A' * x = b.
! 145: *
! 146: DO 30 J = 1, NRHS
! 147: CALL DTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
! 148: 30 CONTINUE
! 149: *
! 150: RETURN
! 151: *
! 152: * End of DTPTRS
! 153: *
! 154: END
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