DLAIC1
Purpose
DLAIC1 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 DLAIC1 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.
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 DLAIC1 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.
Arguments
| JOB |
(input) INTEGER
= 1: an estimate for the largest singular value is computed.
= 2: an estimate for the smallest singular value is computed. |
| J |
(input) INTEGER
Length of X and W
|
| X |
(input) DOUBLE PRECISION array, dimension (J)
The j-vector x.
|
| SEST |
(input) DOUBLE PRECISION
Estimated singular value of j by j matrix L
|
| W |
(input) DOUBLE PRECISION array, dimension (J)
The j-vector w.
|
| GAMMA |
(input) DOUBLE PRECISION
The diagonal element gamma.
|
| SESTPR |
(output) DOUBLE PRECISION
Estimated singular value of (j+1) by (j+1) matrix Lhat.
|
| S |
(output) DOUBLE PRECISION
Sine needed in forming xhat.
|
| C |
(output) DOUBLE PRECISION
Cosine needed in forming xhat.
|