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To set up the proper storage and to arrange for effective use
of the IRAM 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 Arnoldi factorization. This represents
the maximum number of Arnoldi 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.
 [sigmar] The real part of the shift used if a spectral
transformation is employed.
 [sigmai] The imaginary part of 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 an eigenvalue
cluster. The only restriction is that nev must be less than
ncv. The recommended 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.6.
Table A.6:
The eigenvalues of interest for nonsymmetric eigenvalue problems.


which 
EIGENVALUES 


'LM' 
Largest magnitude 
'SM' 
Smallest magnitude 
'LR' 
Largest real parts 
'SR' 
Smallest real parts 
'LI' 
Largest imaginary parts 
'SI' 
Smallest imaginary parts 
When using a spectral transformation, the selection
of which = 'SM' should be avoided.
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+2 

ncv 
are satisfied. The last condition on nev is needed to
assure that complex conjugate pairs of eigenvalues are kept together.
Next: Other Variables
Up: Real Nonsymmetric Drivers
Previous: Driver dndrv6
Chao Yang
11/7/1997