Annotation of rpl/lapack/lapack/dpptrs.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DPPTRS( UPLO, 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 UPLO
! 10: INTEGER INFO, LDB, N, NRHS
! 11: * ..
! 12: * .. Array Arguments ..
! 13: DOUBLE PRECISION AP( * ), B( LDB, * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * DPPTRS solves a system of linear equations A*X = B with a symmetric
! 20: * positive definite matrix A in packed storage using the Cholesky
! 21: * factorization A = U**T*U or A = L*L**T computed by DPPTRF.
! 22: *
! 23: * Arguments
! 24: * =========
! 25: *
! 26: * UPLO (input) CHARACTER*1
! 27: * = 'U': Upper triangle of A is stored;
! 28: * = 'L': Lower triangle of A is stored.
! 29: *
! 30: * N (input) INTEGER
! 31: * The order of the matrix A. N >= 0.
! 32: *
! 33: * NRHS (input) INTEGER
! 34: * The number of right hand sides, i.e., the number of columns
! 35: * of the matrix B. NRHS >= 0.
! 36: *
! 37: * AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
! 38: * The triangular factor U or L from the Cholesky factorization
! 39: * A = U**T*U or A = L*L**T, packed columnwise in a linear
! 40: * array. The j-th column of U or L is stored in the array AP
! 41: * as follows:
! 42: * if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
! 43: * if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
! 44: *
! 45: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
! 46: * On entry, the right hand side matrix B.
! 47: * On exit, the solution matrix X.
! 48: *
! 49: * LDB (input) INTEGER
! 50: * The leading dimension of the array B. LDB >= max(1,N).
! 51: *
! 52: * INFO (output) INTEGER
! 53: * = 0: successful exit
! 54: * < 0: if INFO = -i, the i-th argument had an illegal value
! 55: *
! 56: * =====================================================================
! 57: *
! 58: * .. Local Scalars ..
! 59: LOGICAL UPPER
! 60: INTEGER I
! 61: * ..
! 62: * .. External Functions ..
! 63: LOGICAL LSAME
! 64: EXTERNAL LSAME
! 65: * ..
! 66: * .. External Subroutines ..
! 67: EXTERNAL DTPSV, XERBLA
! 68: * ..
! 69: * .. Intrinsic Functions ..
! 70: INTRINSIC MAX
! 71: * ..
! 72: * .. Executable Statements ..
! 73: *
! 74: * Test the input parameters.
! 75: *
! 76: INFO = 0
! 77: UPPER = LSAME( UPLO, 'U' )
! 78: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 79: INFO = -1
! 80: ELSE IF( N.LT.0 ) THEN
! 81: INFO = -2
! 82: ELSE IF( NRHS.LT.0 ) THEN
! 83: INFO = -3
! 84: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
! 85: INFO = -6
! 86: END IF
! 87: IF( INFO.NE.0 ) THEN
! 88: CALL XERBLA( 'DPPTRS', -INFO )
! 89: RETURN
! 90: END IF
! 91: *
! 92: * Quick return if possible
! 93: *
! 94: IF( N.EQ.0 .OR. NRHS.EQ.0 )
! 95: $ RETURN
! 96: *
! 97: IF( UPPER ) THEN
! 98: *
! 99: * Solve A*X = B where A = U'*U.
! 100: *
! 101: DO 10 I = 1, NRHS
! 102: *
! 103: * Solve U'*X = B, overwriting B with X.
! 104: *
! 105: CALL DTPSV( 'Upper', 'Transpose', 'Non-unit', N, AP,
! 106: $ B( 1, I ), 1 )
! 107: *
! 108: * Solve U*X = B, overwriting B with X.
! 109: *
! 110: CALL DTPSV( 'Upper', 'No transpose', 'Non-unit', N, AP,
! 111: $ B( 1, I ), 1 )
! 112: 10 CONTINUE
! 113: ELSE
! 114: *
! 115: * Solve A*X = B where A = L*L'.
! 116: *
! 117: DO 20 I = 1, NRHS
! 118: *
! 119: * Solve L*Y = B, overwriting B with X.
! 120: *
! 121: CALL DTPSV( 'Lower', 'No transpose', 'Non-unit', N, AP,
! 122: $ B( 1, I ), 1 )
! 123: *
! 124: * Solve L'*X = Y, overwriting B with X.
! 125: *
! 126: CALL DTPSV( 'Lower', 'Transpose', 'Non-unit', N, AP,
! 127: $ B( 1, I ), 1 )
! 128: 20 CONTINUE
! 129: END IF
! 130: *
! 131: RETURN
! 132: *
! 133: * End of DPPTRS
! 134: *
! 135: END
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