Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?laqr1
Sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.
Syntax
call slaqr1 ( n , h , ldh , sr1 , si1 , sr2 , si2, v )
call dlaqr1 ( n , h , ldh , sr1 , si1 , sr2 , si2, v )
call claqr1 ( n , h , ldh , s1 , s2 , v )
call zlaqr1 ( n , h , ldh , s1 , s2 , v )
Include Files
mkl.fi
Description
slaqr1 dlaqr1 claqr1 zlaqr1
Given a 2-by-2 or 3-by-3 matrix H , this routine sets v to a scalar multiple of the first column of the product
K = (H - s1*I)*(H - s2*I) , or K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I)
scaling to avoid overflows and most underflows.
It is assumed that either 1) sr1 = sr2 and si1 = -si2 , or 2) si1 = si2 = 0 .
This is useful for starting double implicit shift bulges in the QR algorithm.
Input Parameters
- n
-
INTEGER . The order of the matrix H . n must be equal to 2 or 3.
- sr1 , si2 , sr2 , si2
-
REAL for slaqr1 DOUBLE PRECISION for dlaqr1 Shift values that define K in the formula above.
- s1 , s2
-
COMPLEX for claqr1 DOUBLE COMPLEX for zlaqr1 .
- h
-
REAL for slaqr1 DOUBLE PRECISION for dlaqr1 COMPLEX for claqr1 DOUBLE COMPLEX for zlaqr1 . Array, DIMENSION ( ldh , n ), contains 2-by-2 or 3-by-3 matrix H in the formula above.
- ldh
-
INTEGER . The leading dimension of the array h just as declared in the calling routine. ldh ≥ n .
Output Parameters
- v
-
REAL for slaqr1 DOUBLE PRECISION for dlaqr1 COMPLEX for claqr1 DOUBLE COMPLEX for zlaqr1 . Array with dimension (n) . A scalar multiple of the first column of the matrix K in the formula above.