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To set up the proper storage and to arrange for effective use
of the IRLM various parameters will have to be set.
These variables include:
<<354>>
 [n] The dimension of the problem.
 [nev] The number of eigenvalues needed.
 [ncv] The length of the Lanczos factorization. This represents
the maximum number of Lanczos vectors used.
 [which] The eigenvalues of interest.
 [info] Set to 0 for a randomly generated starting vector.
If the user decides to use another starting vector,
this value should be set to 1, and the starting vector
should be provided in the array resid.
 [sigma] The shift used if a spectral transformation is employed.
The variable nev may be set to be a value larger than the
number of eigenvalues desired to avoid splitting a eigenvalue
cluster. The only restriction is that nev must be less than
ncv. The recommended initial choice of ncv
is to set ncv = 2 nev.
The user is encouraged to experiment with both nev and ncv.
The possible choices for the input variable which are listed in
Table A.3.
Table A.3:
The eigenvalues of interest for symmetric eigenvalue problems.


which 
EIGENVALUES 


'LA' 
Largest (algebraic) eigenvalues. 
'SA' 
Smallest (algebraic) eigenvalues. 
'LM' 
Largest eigenvalues in magnitude. 
'SM' 
Smallest eigenvalues in magnitude. 
'BE' 
Eigenvalue at both ends. When nev 

is odd, compute one more from the 

high end than from the low end. 
When a spectral transformation is employed,
only the selections
'BE', 'LA' or 'SA' should be used.
Once the above variables are modified, the storage declarations
integer maxn, maxnev, maxncv, ldv
parameter (maxn=256, maxnev=10, maxncv=25, ldv=maxn )
should be adjusted so that the conditions
n 

maxn, 
nev 

maxnev, 
ncv 

maxncv, 
nev + 1 

ncv 
are satisfied.
Next: Other Variables
Up: Symmetric Drivers
Previous: Driver dsdrv6
Chao Yang
11/7/1997