[SciPy-user] help about solver sparse matrix

David Warde-Farley dwf@cs.toronto....
Sat Apr 19 18:49:45 CDT 2008

On 19-Apr-08, at 7:04 PM, Jose Lopez wrote:
> thanks
> but, how to get the number of iterations of the result?

There's no explicit support for this in the cgs method, but it does  
let you pass in a function that gets called after iteration. You  
could therefore use callbacks to keep track of how many iterations  
your solution took. Take a look at the following example: I create an  
object with a method "call" that updates it's internal 'cnt' variable  
every time it gets called. (I commented out the print statement  
because it'd be kind of long in this e-mail.

In [153]: from scipy import *

In [154]: class Counter:
    .....:     def __init__(self):
    .....:         self.cnt = 0
    .....:     def call(self, arg):
    .....:         self.cnt += 1
    .....:         # print "Iteration %3d: sqnorm=%5.4e" % (self.cnt,  

In [155]: c = Counter()

In [156]: A = abs(randn(50,50))

In [157]: A = sparse.csr_matrix(A + A.T)

In [158]: y = splinalg.cgs(A, randn(50), callback=c.call)

In [159]: c.cnt
Out[159]: 82

After that, stored inside the Counter object is the quantity you're  
looking for.



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