Visible to Intel only — GUID: GUID-B8123029-A8CA-4547-8E2F-5BB58C5A4343
Visible to Intel only — GUID: GUID-B8123029-A8CA-4547-8E2F-5BB58C5A4343
?lamsh
Sends multiple shifts through a small (single node) matrix to maximize the number of bulges that can be sent through.
Syntax
call slamsh(s, lds, nbulge, jblk, h, ldh, n, ulp)
call dlamsh(s, lds, nbulge, jblk, h, ldh, n, ulp)
call clamsh(s, lds, nbulge, jblk, h, ldh, n, ulp)
call zlamsh(s, lds, nbulge, jblk, h, ldh, n, ulp)
Description
The ?lamshroutine sends multiple shifts through a small (single node) matrix to see how small consecutive subdiagonal elements are modified by subsequent shifts in an effort to maximize the number of bulges that can be sent through. The subroutine should only be called when there are multiple shifts/bulges (nbulge > 1) and the first shift is starting in the middle of an unreduced Hessenberg matrix because of two or more small consecutive subdiagonal elements.
Input Parameters
- s
-
(local)
REAL for slamsh
DOUBLE PRECISION for dlamsh
COMPLEX for clamsh
DOUBLE COMPLEX for zlamsh
Array of size (lds, 2*jblk).
On entry, the matrix of shifts. Only the 2x2 diagonal of s is referenced. It is assumed that s has jblk double shifts (size 2).
- lds
-
(local) INTEGER.
On entry, the leading dimension of S; unchanged on exit. 1<nbulge ≤ jblk ≤ lds/2.
- nbulge
-
(local) INTEGER.
On entry, the number of bulges to send through h (>1). nbulge should be less than the maximum determined (jblk). 1<nbulge ≤ jblk ≤ lds/2.
- jblk
-
(local) INTEGER.
On entry, the number of double shifts determined for S; unchanged on exit.
- h
-
(local)
REAL for slamsh
DOUBLE PRECISION for dlamsh
COMPLEX for clamsh
DOUBLE COMPLEX for zlamsh
Array of size (ldh, n).
On entry, the local matrix to apply the shifts on.
h should be aligned so that the starting row is 2.
- ldh
-
(local)
INTEGER.
On entry, the leading dimension of H; unchanged on exit.
- n
-
(local) INTEGER.
On entry, the size of H. If all the bulges are expected to go through, n should be at least 4nbulge+2. Otherwise, nbulge may be reduced by this routine.
- ulp
-
(local)
REAL for slamsh
DOUBLE PRECISION for dlamsh
REAL for clamsh
DOUBLE PRECISION for zlamsh
On entry, machine precision. Unchanged on exit.
Output Parameters
- s
-
On exit, the data is rearranged in the best order for applying.
- nbulge
-
On exit, the maximum number of bulges that can be sent through.
- h
-
On exit, the data is destroyed.