SRC/dorm22.f(3) Library Functions Manual SRC/dorm22.f(3)

SRC/dorm22.f


subroutine dorm22 (side, trans, m, n, n1, n2, q, ldq, c, ldc, work, lwork, info)
DORM22 multiplies a general matrix by a banded orthogonal matrix.

DORM22 multiplies a general matrix by a banded orthogonal matrix.

Purpose

  DORM22 overwrites the general real M-by-N matrix C with
                  SIDE = 'L'     SIDE = 'R'
  TRANS = 'N':      Q * C          C * Q
  TRANS = 'T':      Q**T * C       C * Q**T
  where Q is a real orthogonal matrix of order NQ, with NQ = M if
  SIDE = 'L' and NQ = N if SIDE = 'R'.
  The orthogonal matrix Q processes a 2-by-2 block structure
         [  Q11  Q12  ]
     Q = [            ]
         [  Q21  Q22  ],
  where Q12 is an N1-by-N1 lower triangular matrix and Q21 is an
  N2-by-N2 upper triangular matrix.

Parameters

SIDE
          SIDE is CHARACTER*1
          = 'L': apply Q or Q**T from the Left;
          = 'R': apply Q or Q**T from the Right.

TRANS

          TRANS is CHARACTER*1
          = 'N':  apply Q (No transpose);
          = 'C':  apply Q**T (Conjugate transpose).

M

          M is INTEGER
          The number of rows of the matrix C. M >= 0.

N

          N is INTEGER
          The number of columns of the matrix C. N >= 0.

N1
N2

          N1 is INTEGER
          N2 is INTEGER
          The dimension of Q12 and Q21, respectively. N1, N2 >= 0.
          The following requirement must be satisfied:
          N1 + N2 = M if SIDE = 'L' and N1 + N2 = N if SIDE = 'R'.

Q

          Q is DOUBLE PRECISION array, dimension
                                       (LDQ,M) if SIDE = 'L'
                                       (LDQ,N) if SIDE = 'R'

LDQ

          LDQ is INTEGER
          The leading dimension of the array Q.
          LDQ >= max(1,M) if SIDE = 'L'; LDQ >= max(1,N) if SIDE = 'R'.

C

          C is DOUBLE PRECISION array, dimension (LDC,N)
          On entry, the M-by-N matrix C.
          On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q.

LDC

          LDC is INTEGER
          The leading dimension of the array C. LDC >= max(1,M).

WORK

          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK

          LWORK is INTEGER
          The dimension of the array WORK.
          If SIDE = 'L', LWORK >= max(1,N);
          if SIDE = 'R', LWORK >= max(1,M).
          For optimum performance LWORK >= M*N.
          If LWORK = -1, then a workspace query is assumed; the routine
          only calculates the optimal size of the WORK array, returns
          this value as the first entry of the WORK array, and no error
          message related to LWORK is issued by XERBLA.

INFO

          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 161 of file dorm22.f.

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