MATLAB Function Reference 
1norm condition number estimate
Syntax
Description
c = condest(A)
computes a lower bound C for the 1norm condition number of a square matrix A.
c = condest(A,t)
changes t
, a positive integer parameter equal to the number of columns in an underlying iteration matrix. Increasing the number of columns usually gives a better condition estimate but increases the cost. The default is t = 2
, which almost always gives an estimate correct to within a factor 2.
[c,v] = condest(A)
also computes a vector v
which is an approximate null vector if c
is large. v
satisfies norm(A*v,1) = norm(A,1)*norm(v,1)/c
.
Note
condest invokes rand . If repeatable results are required then invoke rand('state',j) , for some j , before calling this function.

This function is particularly useful for sparse matrices.
condest
uses block 1norm power method of Higham and Tisseur [1].
See Also
Reference
[1] Higham, N. J. and F. Tisseur, "A Block Algorithm for Matrix 1Norm Estimation, with an Application to 1Norm Pseudospectra," SIAM Journal Matrix Anal. Appl., Vol. 21, No. 4, 2000, pp.11851201.
condeig  coneplot 
© 19942005 The MathWorks, Inc.