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# rcond

inverse condition number

### Syntax

r = rcond(X)

### Arguments

- X
real or complex square matrix

- r
real positive number

### Description

`rcond(X)`

is an estimate for the reciprocal of the
condition of `X`

in the 1-norm.

If `X`

is well conditioned, `rcond(X)`

is close to 1.
If not, `rcond(X)`

is close to 0.

Estimating the 1-norm inverse condition number with `rcond` is
much faster than computing the 2-norm condition number with `cond` .
As a trade-off, `rcond` may be less reliable. |

Algorithm: We compute the 1-norm of X with Lapack/DLANGE, compute its LU decomposition with Lapack/DGETRF, and finally estimate the condition with Lapack/DGECON.

`rcond([])`

yields `%inf`

.

### See also

### History

Version | Description |

6.0.2 | rcond([]) now yields %inf = 1/cond([]) instead of []. |

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