Annotation of rpl/lapack/lapack/dpptri.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DPPTRI( UPLO, N, AP, 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, N
! 11: * ..
! 12: * .. Array Arguments ..
! 13: DOUBLE PRECISION AP( * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * DPPTRI computes the inverse of a real symmetric positive definite
! 20: * matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
! 21: * computed by DPPTRF.
! 22: *
! 23: * Arguments
! 24: * =========
! 25: *
! 26: * UPLO (input) CHARACTER*1
! 27: * = 'U': Upper triangular factor is stored in AP;
! 28: * = 'L': Lower triangular factor is stored in AP.
! 29: *
! 30: * N (input) INTEGER
! 31: * The order of the matrix A. N >= 0.
! 32: *
! 33: * AP (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
! 34: * On entry, the triangular factor U or L from the Cholesky
! 35: * factorization A = U**T*U or A = L*L**T, packed columnwise as
! 36: * a linear array. The j-th column of U or L is stored in the
! 37: * array AP as follows:
! 38: * if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
! 39: * if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
! 40: *
! 41: * On exit, the upper or lower triangle of the (symmetric)
! 42: * inverse of A, overwriting the input factor U or L.
! 43: *
! 44: * INFO (output) INTEGER
! 45: * = 0: successful exit
! 46: * < 0: if INFO = -i, the i-th argument had an illegal value
! 47: * > 0: if INFO = i, the (i,i) element of the factor U or L is
! 48: * zero, and the inverse could not be computed.
! 49: *
! 50: * =====================================================================
! 51: *
! 52: * .. Parameters ..
! 53: DOUBLE PRECISION ONE
! 54: PARAMETER ( ONE = 1.0D+0 )
! 55: * ..
! 56: * .. Local Scalars ..
! 57: LOGICAL UPPER
! 58: INTEGER J, JC, JJ, JJN
! 59: DOUBLE PRECISION AJJ
! 60: * ..
! 61: * .. External Functions ..
! 62: LOGICAL LSAME
! 63: DOUBLE PRECISION DDOT
! 64: EXTERNAL LSAME, DDOT
! 65: * ..
! 66: * .. External Subroutines ..
! 67: EXTERNAL DSCAL, DSPR, DTPMV, DTPTRI, XERBLA
! 68: * ..
! 69: * .. Executable Statements ..
! 70: *
! 71: * Test the input parameters.
! 72: *
! 73: INFO = 0
! 74: UPPER = LSAME( UPLO, 'U' )
! 75: IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 76: INFO = -1
! 77: ELSE IF( N.LT.0 ) THEN
! 78: INFO = -2
! 79: END IF
! 80: IF( INFO.NE.0 ) THEN
! 81: CALL XERBLA( 'DPPTRI', -INFO )
! 82: RETURN
! 83: END IF
! 84: *
! 85: * Quick return if possible
! 86: *
! 87: IF( N.EQ.0 )
! 88: $ RETURN
! 89: *
! 90: * Invert the triangular Cholesky factor U or L.
! 91: *
! 92: CALL DTPTRI( UPLO, 'Non-unit', N, AP, INFO )
! 93: IF( INFO.GT.0 )
! 94: $ RETURN
! 95: *
! 96: IF( UPPER ) THEN
! 97: *
! 98: * Compute the product inv(U) * inv(U)'.
! 99: *
! 100: JJ = 0
! 101: DO 10 J = 1, N
! 102: JC = JJ + 1
! 103: JJ = JJ + J
! 104: IF( J.GT.1 )
! 105: $ CALL DSPR( 'Upper', J-1, ONE, AP( JC ), 1, AP )
! 106: AJJ = AP( JJ )
! 107: CALL DSCAL( J, AJJ, AP( JC ), 1 )
! 108: 10 CONTINUE
! 109: *
! 110: ELSE
! 111: *
! 112: * Compute the product inv(L)' * inv(L).
! 113: *
! 114: JJ = 1
! 115: DO 20 J = 1, N
! 116: JJN = JJ + N - J + 1
! 117: AP( JJ ) = DDOT( N-J+1, AP( JJ ), 1, AP( JJ ), 1 )
! 118: IF( J.LT.N )
! 119: $ CALL DTPMV( 'Lower', 'Transpose', 'Non-unit', N-J,
! 120: $ AP( JJN ), AP( JJ+1 ), 1 )
! 121: JJ = JJN
! 122: 20 CONTINUE
! 123: END IF
! 124: *
! 125: RETURN
! 126: *
! 127: * End of DPPTRI
! 128: *
! 129: END
CVSweb interface <joel.bertrand@systella.fr>