MA02CD

Pertransposing the central band of a square matrix

Purpose

  To compute the pertranspose of a central band of a square matrix.

      SUBROUTINE MA02CD( N, KL, KU, A, LDA )
C     .. Scalar Arguments ..
      INTEGER          KL, KU, LDA, N
C     .. Array Arguments ..
      DOUBLE PRECISION A(LDA,*)

Input/Output Parameters

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

  KL      (input) INTEGER
          The number of subdiagonals of A to be pertransposed.
          0 <= KL <= N-1.

  KU      (input) INTEGER
          The number of superdiagonals of A to be pertransposed.
          0 <= KU <= N-1.

  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
          On entry, the leading N-by-N part of this array must
          contain a square matrix whose central band formed from
          the KL subdiagonals, the main diagonal and the KU
          superdiagonals will be pertransposed.
          On exit, the leading N-by-N part of this array contains
          the matrix A with its central band (the KL subdiagonals,
          the main diagonal and the KU superdiagonals) pertransposed
          (that is the elements of each antidiagonal appear in
          reversed order). This is equivalent to forming P*B'*P,
          where B is the matrix formed from the central band of A
          and P is a permutation matrix with ones down the secondary
          diagonal.

  LDA     INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).

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Program Text

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