MB03BE

Applying iterations of a real single shifted periodic QZ algorithm to a 2-by-2 matrix product

Purpose

  To apply at most 20 iterations of a real single shifted
  periodic QZ algorithm to the 2-by-2 product of matrices stored
  in the array A.

      SUBROUTINE MB03BE( K, AMAP, S, SINV, A, LDA1, LDA2 )
C     .. Scalar Arguments ..
      INTEGER           K, LDA1, LDA2, SINV
C     .. Array Arguments ..
      INTEGER           AMAP(*), S(*)
      DOUBLE PRECISION  A(LDA1,LDA2,*)

Input/Output Parameters

  K       (input)  INTEGER
          The number of factors.  K >= 1.

  AMAP    (input)  INTEGER array, dimension (K)
          The map for accessing the factors, i.e., if AMAP(I) = J,
          then the factor A_I is stored at the J-th position in A.

  S       (input)  INTEGER array, dimension (K)
          The signature array. Each entry of S must be 1 or -1.

  SINV    (input)  INTEGER
          Signature multiplier. Entries of S are virtually
          multiplied by SINV.

  A       (input/output)  DOUBLE PRECISION array, dimension
                          (LDA1,LDA2,K)
          On entry, the leading 2-by-2-by-K part of this array must
          contain a 2-by-2 product (implicitly represented by its K
          factors) in upper Hessenberg form.
          On exit, the leading 2-by-2-by-K part of this array
          contains the product after at most 20 iterations of a real
          shifted periodic QZ algorithm.

  LDA1    INTEGER
          The first leading dimension of the array A.  LDA1 >= 2.

  LDA2    INTEGER
          The second leading dimension of the array A.  LDA2 >= 2.

  Ten iterations of a real single shifted periodic QZ algorithm are
  applied to the 2-by-2 matrix product A.

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Program Text

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