# condest

## Purpose

1-norm matrix condition number estimate.

## Synopsis

    c = condest(A)
    [c,v] = condest(A)
    [c,v] = condest(A,trace)

## Description

`c = condest(A)` uses Higham's modification of Hager's method to estimate the condition number of a matrix. The computed `c` is a lower bound for the condition of `A` in the 1-norm.

`[c,v] = condest(A)` also computes a vector `v` such that

Thus, `v` is an approximate null vector of `A` if `c` is large.

`[c,v] = condest(A,trace)` provides further information about the estimate, where trace can be:

- 1 to print information about each step of the iteration.
- -1 to print the ratios of the estimate to the actual (computed) condition number and to `rcond`.
  This function handles both real and complex matrices. It is particularly useful (without `trace = -1`) for sparse matrices.

  ## See Also

      cond, normest, rcond

  ## Reference

  [1] N.J. Higham, FORTRAN codes for estimating the one-norm of a real or complex matrix, with applications to condition estimation, ACM Trans. Math. Soft., 14, pp. 381-396 (1988).

  (c) Copyright 1994 by The MathWorks, Inc.