Sign up ×
MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.

This is probably a basic question, but my linear algebra is weak.

Suppose I want to compute the nullspace of a matrix A using some iterative method (e.g. Lanczos). Suppose further that I know a priori the nullspace of the first n columns of the matrix, i.e., Av = [0 0 0 ... 0 b_n .. B_N], where b_i are nonzero with high probability.

Does starting the iterative method with vector v (instead of a random vector) speed the iterative method (e.g., Lanczos) up at all?

share|cite|improve this question

1 Answer 1


You will need to apply $A$ fewer times to get the linear dependence of the rightmost columns.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.