Previous: stbrfs Up: ../lapack-s.html Next: stgevc

stbtrs

 NAME
      STBTRS - solve a triangular system of the form   A * X = B
      or A**T * X = B,

 SYNOPSIS
      SUBROUTINE STBTRS( UPLO, TRANS, DIAG, N, KD, NRHS, AB, LDAB,
                         B, LDB, INFO )

          CHARACTER      DIAG, TRANS, UPLO

          INTEGER        INFO, KD, LDAB, LDB, N, NRHS

          REAL           AB( LDAB, * ), B( LDB, * )

 PURPOSE
      STBTRS solves a triangular system of the form

      where A is a triangular band matrix of order N, and B is an
      N-by NRHS matrix.  A check is made to verify that A is non-
      singular.

 ARGUMENTS
      UPLO    (input) CHARACTER*1
              = 'U':  A is upper triangular;
              = 'L':  A is lower triangular.

      TRANS   (input) CHARACTER*1
              Specifies the form the system of equations:
              = 'N':  A * X = B  (No transpose)
              = 'T':  A**T * X = B  (Transpose)
              = 'C':  A**H * X = B  (Conjugate transpose = Tran-
              spose)

      DIAG    (input) CHARACTER*1
              = 'N':  A is non-unit triangular;
              = 'U':  A is unit triangular.

      N       (input) INTEGER
              The order of the matrix A.  N >= 0.

      KD      (input) INTEGER
              The number of superdiagonals or subdiagonals of the
              triangular band matrix A.  KD >= 0.

      NRHS    (input) INTEGER
              The number of right hand sides, i.e., the number of
              columns of the matrix B.  NRHS >= 0.

      AB      (input) REAL array, dimension (LDAB,N)
              The upper or lower triangular band matrix A, stored
              in the first kd+1 rows of AB.  The j-th column of A

              is stored in the j-th column of the array AB as fol-
              lows: if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for
              max(1,j-kd)<=i<=j; if UPLO = 'L', AB(1+i-j,j)    =
              A(i,j) for j<=i<=min(n,j+kd).  If DIAG = 'U', the
              diagonal elements of A are not referenced and are
              assumed to be 1.

      LDAB    (input) INTEGER
              The leading dimension of the array AB.  LDAB >=
              KD+1.

      B       (input/output) REAL array, dimension (LDB,NRHS)
              On entry, the right hand side matrix B.  On exit, if
              INFO = 0, the solution matrix X.

      LDB     (input) INTEGER
              The leading dimension of the array B.  LDB >=
              max(1,N).

      INFO    (output) INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal
              value
              > 0:  if INFO = i, the i-th diagonal element of A is
              zero, indicating that the matrix is singular and the
              solutions X have not been computed.