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. The Hessenberg matrix is the last one of the formal matrix product.Specification
SUBROUTINE MB03BF( K, AMAP, S, SINV, A, LDA1, LDA2, ULP ) C .. Scalar Arguments .. INTEGER K, LDA1, LDA2, SINV DOUBLE PRECISION ULP C .. Array Arguments .. INTEGER AMAP(*), S(*) DOUBLE PRECISION A(LDA1,LDA2,*)Arguments
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. The Hessenberg matrix is the last one of the formal matrix product. 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. ULP INTEGER The machine relation precision.Method
Twenty iterations of a real single shifted periodic QZ algorithm are applied to the 2-by-2 matrix product A.Further Comments
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