SLAIC1 (3) - Linux Manuals
subroutine slaic1 (integerJOB, integerJ, real, dimension( j )X, realSEST, real, dimension( j )W, realGAMMA, realSESTPR, realS, realC)
SLAIC1 applies one step of incremental condition estimation.
SLAIC1 applies one step of incremental condition estimation in its simplest version: Let x, twonorm(x) = 1, be an approximate singular vector of an j-by-j lower triangular matrix L, such that twonorm(L*x) = sest Then SLAIC1 computes sestpr, s, c such that the vector [ s*x ] xhat = [ c ] is an approximate singular vector of [ L 0 ] Lhat = [ w**T gamma ] in the sense that twonorm(Lhat*xhat) = sestpr. Depending on JOB, an estimate for the largest or smallest singular value is computed. Note that [s c]**T and sestpr**2 is an eigenpair of the system diag(sest*sest, 0) + [alpha gamma] * [ alpha ] [ gamma ] where alpha = x**T*w.
JOB is INTEGER = 1: an estimate for the largest singular value is computed. = 2: an estimate for the smallest singular value is computed.
J is INTEGER Length of X and W
X is REAL array, dimension (J) The j-vector x.
SEST is REAL Estimated singular value of j by j matrix L
W is REAL array, dimension (J) The j-vector w.
GAMMA is REAL The diagonal element gamma.
SESTPR is REAL Estimated singular value of (j+1) by (j+1) matrix Lhat.
S is REAL Sine needed in forming xhat.
C is REAL Cosine needed in forming xhat.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
- September 2012
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