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[Lapack] fast condition number of nonsquare matrix

 Does DTRCON modify any entry in its input matrix "A" ?
It is not mentioned in it's manual page that it makes
any modification to "A", but I ask to be sure.

Thank you, regards,

Quoting Julien Langou:
(1) first, compute a QR factorization of your matrix A, if A is m-by-n, 
this will cost you 2m*n^2-2/3*n^3, this is done with DGEQRF

(2) the 2-norm condition number of A and the 2-norm condition number of R 
will then be the same, so you compute the condition number of R with 
DTRCON, this cost a few n^2. You can choose the norm in which you want the 

I want to get a fast approximation for a condition number
of a general non square matrix. Or at least it's smaller

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