Annotation of rpl/lapack/lapack/zposv.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE ZPOSV( UPLO, N, NRHS, A, LDA, B, LDB, INFO )
! 2: *
! 3: * -- LAPACK driver 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 UPLO
! 10: INTEGER INFO, LDA, LDB, N, NRHS
! 11: * ..
! 12: * .. Array Arguments ..
! 13: COMPLEX*16 A( LDA, * ), B( LDB, * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * ZPOSV computes the solution to a complex system of linear equations
! 20: * A * X = B,
! 21: * where A is an N-by-N Hermitian positive definite matrix and X and B
! 22: * are N-by-NRHS matrices.
! 23: *
! 24: * The Cholesky decomposition is used to factor A as
! 25: * A = U**H* U, if UPLO = 'U', or
! 26: * A = L * L**H, if UPLO = 'L',
! 27: * where U is an upper triangular matrix and L is a lower triangular
! 28: * matrix. The factored form of A is then used to solve the system of
! 29: * equations A * X = B.
! 30: *
! 31: * Arguments
! 32: * =========
! 33: *
! 34: * UPLO (input) CHARACTER*1
! 35: * = 'U': Upper triangle of A is stored;
! 36: * = 'L': Lower triangle of A is stored.
! 37: *
! 38: * N (input) INTEGER
! 39: * The number of linear equations, i.e., the order of the
! 40: * matrix A. N >= 0.
! 41: *
! 42: * NRHS (input) INTEGER
! 43: * The number of right hand sides, i.e., the number of columns
! 44: * of the matrix B. NRHS >= 0.
! 45: *
! 46: * A (input/output) COMPLEX*16 array, dimension (LDA,N)
! 47: * On entry, the Hermitian matrix A. If UPLO = 'U', the leading
! 48: * N-by-N upper triangular part of A contains the upper
! 49: * triangular part of the matrix A, and the strictly lower
! 50: * triangular part of A is not referenced. If UPLO = 'L', the
! 51: * leading N-by-N lower triangular part of A contains the lower
! 52: * triangular part of the matrix A, and the strictly upper
! 53: * triangular part of A is not referenced.
! 54: *
! 55: * On exit, if INFO = 0, the factor U or L from the Cholesky
! 56: * factorization A = U**H*U or A = L*L**H.
! 57: *
! 58: * LDA (input) INTEGER
! 59: * The leading dimension of the array A. LDA >= max(1,N).
! 60: *
! 61: * B (input/output) COMPLEX*16 array, dimension (LDB,NRHS)
! 62: * On entry, the N-by-NRHS right hand side matrix B.
! 63: * On exit, if INFO = 0, the N-by-NRHS solution matrix X.
! 64: *
! 65: * LDB (input) INTEGER
! 66: * The leading dimension of the array B. LDB >= max(1,N).
! 67: *
! 68: * INFO (output) INTEGER
! 69: * = 0: successful exit
! 70: * < 0: if INFO = -i, the i-th argument had an illegal value
! 71: * > 0: if INFO = i, the leading minor of order i of A is not
! 72: * positive definite, so the factorization could not be
! 73: * completed, and the solution has not been computed.
! 74: *
! 75: * =====================================================================
! 76: *
! 77: * .. External Functions ..
! 78: LOGICAL LSAME
! 79: EXTERNAL LSAME
! 80: * ..
! 81: * .. External Subroutines ..
! 82: EXTERNAL XERBLA, ZPOTRF, ZPOTRS
! 83: * ..
! 84: * .. Intrinsic Functions ..
! 85: INTRINSIC MAX
! 86: * ..
! 87: * .. Executable Statements ..
! 88: *
! 89: * Test the input parameters.
! 90: *
! 91: INFO = 0
! 92: IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 93: INFO = -1
! 94: ELSE IF( N.LT.0 ) THEN
! 95: INFO = -2
! 96: ELSE IF( NRHS.LT.0 ) THEN
! 97: INFO = -3
! 98: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
! 99: INFO = -5
! 100: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
! 101: INFO = -7
! 102: END IF
! 103: IF( INFO.NE.0 ) THEN
! 104: CALL XERBLA( 'ZPOSV ', -INFO )
! 105: RETURN
! 106: END IF
! 107: *
! 108: * Compute the Cholesky factorization A = U'*U or A = L*L'.
! 109: *
! 110: CALL ZPOTRF( UPLO, N, A, LDA, INFO )
! 111: IF( INFO.EQ.0 ) THEN
! 112: *
! 113: * Solve the system A*X = B, overwriting B with X.
! 114: *
! 115: CALL ZPOTRS( UPLO, N, NRHS, A, LDA, B, LDB, INFO )
! 116: *
! 117: END IF
! 118: RETURN
! 119: *
! 120: * End of ZPOSV
! 121: *
! 122: END
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