SRC/stbtrs.f(3)

NAME
SRC/stbtrs.f

SYNOPSIS

  Functions/Subroutines
subroutine stbtrs (uplo, trans, diag, n, kd, nrhs, ab, ldab, b, ldb, info)
STBTRS

Function/Subroutine Documentation

  subroutine stbtrs (character uplo, character trans, character diag, integer n, integer kd, integer nrhs, real, dimension( ldab, * ) ab, integer ldab, real, dimension( ldb, * ) b, integer ldb, integer info)

STBTRS

Purpose:

    !>
    !> STBTRS solves a triangular system of the form
    !>
    !>    A * X = B  or  A**T * X = B,
    !>
    !> where A is a triangular band matrix of order N, and B is an N-by-NRHS matrix.
    !>
    !> This subroutine verifies that A is nonsingular, but callers should note that only exact
    !> singularity is detected. It is conceivable for one or more diagonal elements of A to be
    !> subnormally tiny numbers without this subroutine signalling an error.
    !>
    !> If a possible loss of numerical precision due to near-singular matrices is a concern, the
    !> caller should verify that A is nonsingular within some tolerance before calling this subroutine.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  A is upper triangular;
    !>          = 'L':  A is lower triangular.
    !>

    TRANS

    !>          TRANS is 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 = Transpose)
    !>

    DIAG

    !>          DIAG is CHARACTER*1
    !>          = 'N':  A is non-unit triangular;
    !>          = 'U':  A is unit triangular.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    KD

    !>          KD is INTEGER
    !>          The number of superdiagonals or subdiagonals of the
    !>          triangular band matrix A.  KD >= 0.
    !>

    NRHS

    !>          NRHS is INTEGER
    !>          The number of right hand sides, i.e., the number of columns
    !>          of the matrix B.  NRHS >= 0.
    !>

    AB

    !>          AB is 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 follows:
    !>          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

    !>          LDAB is INTEGER
    !>          The leading dimension of the array AB.  LDAB >= KD+1.
    !>

    B

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

    LDB

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

    INFO

    !>          INFO is 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 exactly zero,
    !>                indicating that the matrix is singular and the
    !>                solutions X have not been computed.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 150 of file stbtrs.f.

Author

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