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Annotation of rpl/lapack/lapack/zptsv.f, revision 1.3

1.1       bertrand    1:       SUBROUTINE ZPTSV( N, NRHS, D, E, 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:       INTEGER            INFO, LDB, N, NRHS
                     10: *     ..
                     11: *     .. Array Arguments ..
                     12:       DOUBLE PRECISION   D( * )
                     13:       COMPLEX*16         B( LDB, * ), E( * )
                     14: *     ..
                     15: *
                     16: *  Purpose
                     17: *  =======
                     18: *
                     19: *  ZPTSV computes the solution to a complex system of linear equations
                     20: *  A*X = B, where A is an N-by-N Hermitian positive definite tridiagonal
                     21: *  matrix, and X and B are N-by-NRHS matrices.
                     22: *
                     23: *  A is factored as A = L*D*L**H, and the factored form of A is then
                     24: *  used to solve the system of equations.
                     25: *
                     26: *  Arguments
                     27: *  =========
                     28: *
                     29: *  N       (input) INTEGER
                     30: *          The order of the matrix A.  N >= 0.
                     31: *
                     32: *  NRHS    (input) INTEGER
                     33: *          The number of right hand sides, i.e., the number of columns
                     34: *          of the matrix B.  NRHS >= 0.
                     35: *
                     36: *  D       (input/output) DOUBLE PRECISION array, dimension (N)
                     37: *          On entry, the n diagonal elements of the tridiagonal matrix
                     38: *          A.  On exit, the n diagonal elements of the diagonal matrix
                     39: *          D from the factorization A = L*D*L**H.
                     40: *
                     41: *  E       (input/output) COMPLEX*16 array, dimension (N-1)
                     42: *          On entry, the (n-1) subdiagonal elements of the tridiagonal
                     43: *          matrix A.  On exit, the (n-1) subdiagonal elements of the
                     44: *          unit bidiagonal factor L from the L*D*L**H factorization of
                     45: *          A.  E can also be regarded as the superdiagonal of the unit
                     46: *          bidiagonal factor U from the U**H*D*U factorization of A.
                     47: *
                     48: *  B       (input/output) COMPLEX*16 array, dimension (LDB,N)
                     49: *          On entry, the N-by-NRHS right hand side matrix B.
                     50: *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
                     51: *
                     52: *  LDB     (input) INTEGER
                     53: *          The leading dimension of the array B.  LDB >= max(1,N).
                     54: *
                     55: *  INFO    (output) INTEGER
                     56: *          = 0:  successful exit
                     57: *          < 0:  if INFO = -i, the i-th argument had an illegal value
                     58: *          > 0:  if INFO = i, the leading minor of order i is not
                     59: *                positive definite, and the solution has not been
                     60: *                computed.  The factorization has not been completed
                     61: *                unless i = N.
                     62: *
                     63: *  =====================================================================
                     64: *
                     65: *     .. External Subroutines ..
                     66:       EXTERNAL           XERBLA, ZPTTRF, ZPTTRS
                     67: *     ..
                     68: *     .. Intrinsic Functions ..
                     69:       INTRINSIC          MAX
                     70: *     ..
                     71: *     .. Executable Statements ..
                     72: *
                     73: *     Test the input parameters.
                     74: *
                     75:       INFO = 0
                     76:       IF( N.LT.0 ) THEN
                     77:          INFO = -1
                     78:       ELSE IF( NRHS.LT.0 ) THEN
                     79:          INFO = -2
                     80:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
                     81:          INFO = -6
                     82:       END IF
                     83:       IF( INFO.NE.0 ) THEN
                     84:          CALL XERBLA( 'ZPTSV ', -INFO )
                     85:          RETURN
                     86:       END IF
                     87: *
                     88: *     Compute the L*D*L' (or U'*D*U) factorization of A.
                     89: *
                     90:       CALL ZPTTRF( N, D, E, INFO )
                     91:       IF( INFO.EQ.0 ) THEN
                     92: *
                     93: *        Solve the system A*X = B, overwriting B with X.
                     94: *
                     95:          CALL ZPTTRS( 'Lower', N, NRHS, D, E, B, LDB, INFO )
                     96:       END IF
                     97:       RETURN
                     98: *
                     99: *     End of ZPTSV
                    100: *
                    101:       END