SRC/dtfsm.f(3)

NAME
SRC/dtfsm.f

SYNOPSIS

  Functions/Subroutines
subroutine dtfsm (transr, side, uplo, trans, diag, m, n, alpha, a, b, ldb)
DTFSM solves a matrix equation (one operand is a triangular matrix in RFP format).

Function/Subroutine Documentation

  subroutine dtfsm (character transr, character side, character uplo, character trans, character diag, integer m, integer n, double precision alpha, double precision, dimension( 0: * ) a, double precision, dimension( 0: ldb-1, 0: * ) b, integer ldb)

DTFSM solves a matrix equation (one operand is a triangular matrix in RFP format).

Purpose:

    !>
    !> Level 3 BLAS like routine for A in RFP Format.
    !>
    !> DTFSM  solves the matrix equation
    !>
    !>    op( A )*X = alpha*B  or  X*op( A ) = alpha*B
    !>
    !> where alpha is a scalar, X and B are m by n matrices, A is a unit, or
    !> non-unit,  upper or lower triangular matrix  and  op( A )  is one  of
    !>
    !>    op( A ) = A   or   op( A ) = A**T.
    !>
    !> A is in Rectangular Full Packed (RFP) Format.
    !>
    !> The matrix X is overwritten on B.
    !>

Parameters
    TRANSR

    !>          TRANSR is CHARACTER*1
    !>          = 'N':  The Normal Form of RFP A is stored;
    !>          = 'T':  The Transpose Form of RFP A is stored.
    !>

    SIDE

    !>          SIDE is CHARACTER*1
    !>           On entry, SIDE specifies whether op( A ) appears on the left
    !>           or right of X as follows:
    !>
    !>              SIDE = 'L' or 'l'   op( A )*X = alpha*B.
    !>
    !>              SIDE = 'R' or 'r'   X*op( A ) = alpha*B.
    !>
    !>           Unchanged on exit.
    !>

    UPLO

    !>          UPLO is CHARACTER*1
    !>           On entry, UPLO specifies whether the RFP matrix A came from
    !>           an upper or lower triangular matrix as follows:
    !>           UPLO = 'U' or 'u' RFP A came from an upper triangular matrix
    !>           UPLO = 'L' or 'l' RFP A came from a  lower triangular matrix
    !>
    !>           Unchanged on exit.
    !>

    TRANS

    !>          TRANS is CHARACTER*1
    !>           On entry, TRANS  specifies the form of op( A ) to be used
    !>           in the matrix multiplication as follows:
    !>
    !>              TRANS  = 'N' or 'n'   op( A ) = A.
    !>
    !>              TRANS  = 'T' or 't'   op( A ) = A'.
    !>
    !>           Unchanged on exit.
    !>

    DIAG

    !>          DIAG is CHARACTER*1
    !>           On entry, DIAG specifies whether or not RFP A is unit
    !>           triangular as follows:
    !>
    !>              DIAG = 'U' or 'u'   A is assumed to be unit triangular.
    !>
    !>              DIAG = 'N' or 'n'   A is not assumed to be unit
    !>                                  triangular.
    !>
    !>           Unchanged on exit.
    !>

    M

    !>          M is INTEGER
    !>           On entry, M specifies the number of rows of B. M must be at
    !>           least zero.
    !>           Unchanged on exit.
    !>

    N

    !>          N is INTEGER
    !>           On entry, N specifies the number of columns of B.  N must be
    !>           at least zero.
    !>           Unchanged on exit.
    !>

    ALPHA

    !>          ALPHA is DOUBLE PRECISION
    !>           On entry,  ALPHA specifies the scalar  alpha. When  alpha is
    !>           zero then  A is not referenced and  B need not be set before
    !>           entry.
    !>           Unchanged on exit.
    !>

    A

    !>          A is DOUBLE PRECISION array, dimension (NT)
    !>           NT = N*(N+1)/2 if SIDE='R' and NT = M*(M+1)/2 otherwise.
    !>           On entry, the matrix A in RFP Format.
    !>           RFP Format is described by TRANSR, UPLO and N as follows:
    !>           If TRANSR='N' then RFP A is (0:N,0:K-1) when N is even;
    !>           K=N/2. RFP A is (0:N-1,0:K) when N is odd; K=N/2. If
    !>           TRANSR = 'T' then RFP is the transpose of RFP A as
    !>           defined when TRANSR = 'N'. The contents of RFP A are defined
    !>           by UPLO as follows: If UPLO = 'U' the RFP A contains the NT
    !>           elements of upper packed A either in normal or
    !>           transpose Format. If UPLO = 'L' the RFP A contains
    !>           the NT elements of lower packed A either in normal or
    !>           transpose Format. The LDA of RFP A is (N+1)/2 when
    !>           TRANSR = 'T'. When TRANSR is 'N' the LDA is N+1 when N is
    !>           even and is N when is odd.
    !>           See the Note below for more details. Unchanged on exit.
    !>

    B

    !>          B is DOUBLE PRECISION array, dimension (LDB,N)
    !>           Before entry,  the leading  m by n part of the array  B must
    !>           contain  the  right-hand  side  matrix  B,  and  on exit  is
    !>           overwritten by the solution matrix  X.
    !>

    LDB

    !>          LDB is INTEGER
    !>           On entry, LDB specifies the first dimension of B as declared
    !>           in  the  calling  (sub)  program.   LDB  must  be  at  least
    !>           max( 1, m ).
    !>           Unchanged on exit.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  We first consider Rectangular Full Packed (RFP) Format when N is
    !>  even. We give an example where N = 6.
    !>
    !>      AP is Upper             AP is Lower
    !>
    !>   00 01 02 03 04 05       00
    !>      11 12 13 14 15       10 11
    !>         22 23 24 25       20 21 22
    !>            33 34 35       30 31 32 33
    !>               44 45       40 41 42 43 44
    !>                  55       50 51 52 53 54 55
    !>
    !>
    !>  Let TRANSR = 'N'. RFP holds AP as follows:
    !>  For UPLO = 'U' the upper trapezoid A(0:5,0:2) consists of the last
    !>  three columns of AP upper. The lower triangle A(4:6,0:2) consists of
    !>  the transpose of the first three columns of AP upper.
    !>  For UPLO = 'L' the lower trapezoid A(1:6,0:2) consists of the first
    !>  three columns of AP lower. The upper triangle A(0:2,0:2) consists of
    !>  the transpose of the last three columns of AP lower.
    !>  This covers the case N even and TRANSR = 'N'.
    !>
    !>         RFP A                   RFP A
    !>
    !>        03 04 05                33 43 53
    !>        13 14 15                00 44 54
    !>        23 24 25                10 11 55
    !>        33 34 35                20 21 22
    !>        00 44 45                30 31 32
    !>        01 11 55                40 41 42
    !>        02 12 22                50 51 52
    !>
    !>  Now let TRANSR = 'T'. RFP A in both UPLO cases is just the
    !>  transpose of RFP A above. One therefore gets:
    !>
    !>
    !>           RFP A                   RFP A
    !>
    !>     03 13 23 33 00 01 02    33 00 10 20 30 40 50
    !>     04 14 24 34 44 11 12    43 44 11 21 31 41 51
    !>     05 15 25 35 45 55 22    53 54 55 22 32 42 52
    !>
    !>
    !>  We then consider Rectangular Full Packed (RFP) Format when N is
    !>  odd. We give an example where N = 5.
    !>
    !>     AP is Upper                 AP is Lower
    !>
    !>   00 01 02 03 04              00
    !>      11 12 13 14              10 11
    !>         22 23 24              20 21 22
    !>            33 34              30 31 32 33
    !>               44              40 41 42 43 44
    !>
    !>
    !>  Let TRANSR = 'N'. RFP holds AP as follows:
    !>  For UPLO = 'U' the upper trapezoid A(0:4,0:2) consists of the last
    !>  three columns of AP upper. The lower triangle A(3:4,0:1) consists of
    !>  the transpose of the first two columns of AP upper.
    !>  For UPLO = 'L' the lower trapezoid A(0:4,0:2) consists of the first
    !>  three columns of AP lower. The upper triangle A(0:1,1:2) consists of
    !>  the transpose of the last two columns of AP lower.
    !>  This covers the case N odd and TRANSR = 'N'.
    !>
    !>         RFP A                   RFP A
    !>
    !>        02 03 04                00 33 43
    !>        12 13 14                10 11 44
    !>        22 23 24                20 21 22
    !>        00 33 34                30 31 32
    !>        01 11 44                40 41 42
    !>
    !>  Now let TRANSR = 'T'. RFP A in both UPLO cases is just the
    !>  transpose of RFP A above. One therefore gets:
    !>
    !>           RFP A                   RFP A
    !>
    !>     02 12 22 00 01             00 10 20 30 40 50
    !>     03 13 23 33 11             33 11 21 31 41 51
    !>     04 14 24 34 44             43 44 22 32 42 52
    !>

Definition at line 276 of file dtfsm.f.

Author

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