|MATLAB Function Reference|
1-norm condition number estimate
c = condest(A)
computes a lower bound C for the 1-norm condition number of a square matrix A.
c = condest(A,t)
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.
norm(A*v,1) = norm(A,1)*norm(v,1)/c.
This function is particularly useful for sparse matrices.
condest uses block 1-norm power method of Higham and Tisseur .
 Higham, N. J. and F. Tisseur, "A Block Algorithm for Matrix 1-Norm Estimation, with an Application to 1-Norm Pseudospectra," SIAM Journal Matrix Anal. Appl., Vol. 21, No. 4, 2000, pp.1185-1201.