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---
:name: claqr1
:md5sum: 3f19c2453a865a3b2236f6174de113ff
:category: :subroutine
:arguments:
- n:
:type: integer
:intent: input
- h:
:type: complex
:intent: input
:dims:
- ldh
- n
- ldh:
:type: integer
:intent: input
- s1:
:type: complex
:intent: input
- s2:
:type: complex
:intent: input
- v:
:type: complex
:intent: output
:dims:
- n
:substitutions: {}
:fortran_help: " SUBROUTINE CLAQR1( N, H, LDH, S1, S2, V )\n\n\
* Given a 2-by-2 or 3-by-3 matrix H, CLAQR1 sets v to a\n\
* scalar multiple of the first column of the product\n\
*\n\
* (*) K = (H - s1*I)*(H - s2*I)\n\
*\n\
* scaling to avoid overflows and most underflows.\n\
*\n\
* This is useful for starting double implicit shift bulges\n\
* in the QR algorithm.\n\
*\n\
*\n\n\
* N (input) integer\n\
* Order of the matrix H. N must be either 2 or 3.\n\
*\n\
* H (input) COMPLEX array of dimension (LDH,N)\n\
* The 2-by-2 or 3-by-3 matrix H in (*).\n\
*\n\
* LDH (input) integer\n\
* The leading dimension of H as declared in\n\
* the calling procedure. LDH.GE.N\n\
*\n\
* S1 (input) COMPLEX\n\
* S2 S1 and S2 are the shifts defining K in (*) above.\n\
*\n\
* V (output) COMPLEX array of dimension N\n\
* A scalar multiple of the first column of the\n\
* matrix K in (*).\n\
*\n\n\
* ================================================================\n\
* Based on contributions by\n\
* Karen Braman and Ralph Byers, Department of Mathematics,\n\
* University of Kansas, USA\n\
*\n\
* ================================================================\n\
*\n"
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