# iparmq (l) - Linux Man Pages

## iparmq: This program sets problem and machine dependent parameters useful for xHSEQR and its subroutines

## NAME

IPARMQ - This program sets problem and machine dependent parameters useful for xHSEQR and its subroutines## SYNOPSIS

- INTEGER FUNCTION
- IPARMQ( ISPEC, NAME, OPTS, N, ILO, IHI, LWORK )

- INTEGER IHI, ILO, ISPEC, LWORK, N

- CHARACTER NAME*( * ), OPTS*( * )

## PURPOSE

## ARGUMENTS

- ISPEC (input) integer scalar
- ISPEC specifies which tunable parameter IPARMQ should return. ISPEC=12: (INMIN) Matrices of order nmin or less are sent directly to xLAHQR, the implicit double shift QR algorithm. NMIN must be at least 11. ISPEC=13: (INWIN) Size of the deflation window. This is best set greater than or equal to the number of simultaneous shifts NS. Larger matrices benefit from larger deflation windows. ISPEC=14: (INIBL) Determines when to stop nibbling and invest in an (expensive) multi-shift QR sweep. If the aggressive early deflation subroutine finds LD converged eigenvalues from an order NW deflation window and LD.GT.(NW*NIBBLE)/100, then the next QR sweep is skipped and early deflation is applied immediately to the remaining active diagonal block. Setting IPARMQ(ISPEC=14) = 0 causes TTQRE to skip a multi-shift QR sweep whenever early deflation finds a converged eigenvalue. Setting IPARMQ(ISPEC=14) greater than or equal to 100 prevents TTQRE from skipping a multi-shift QR sweep. ISPEC=15: (NSHFTS) The number of simultaneous shifts in a multi-shift QR iteration. ISPEC=16: (IACC22) IPARMQ is set to 0, 1 or 2 with the following meanings. 0: During the multi-shift QR sweep, xLAQR5 does not accumulate reflections and does not use matrix-matrix multiply to update the far-from-diagonal matrix entries. 1: During the multi-shift QR sweep, xLAQR5 and/or xLAQRaccumulates reflections and uses matrix-matrix multiply to update the far-from-diagonal matrix entries. 2: During the multi-shift QR sweep. xLAQR5 accumulates reflections and takes advantage of 2-by-2 block structure during matrix-matrix multiplies. (If xTRMM is slower than xGEMM, then IPARMQ(ISPEC=16)=1 may be more efficient than IPARMQ(ISPEC=16)=2 despite the greater level of arithmetic work implied by the latter choice.)
- NAME (input) character string
- Name of the calling subroutine
- OPTS (input) character string
- This is a concatenation of the string arguments to TTQRE.
- N (input) integer scalar
- N is the order of the Hessenberg matrix H.
- ILO (input) INTEGER
- IHI (input) INTEGER It is assumed that H is already upper triangular in rows and columns 1:ILO-1 and IHI+1:N.
- LWORK (input) integer scalar
- The amount of workspace available.