[SciPy-user] Matlab's economy size QR decomposition

Travis Oliphant oliphant at ee.byu.edu
Fri Oct 21 00:20:44 CDT 2005


Rick Muller wrote:

>I'm trying to mimic matlabs "economy size" qr decomposition in scipy.  
>Does anyone know how to achieve this using scipy.linalg.qr?
>
>If I call
>     q,r = qr(A)
>Can I then do something like say
>       q = q[:A.shape[0]]
>or something along these lines?
>  
>
Yes, something like that.  Presumably you are after the just the columns 
of q corresponding to the non-zero rows of r.

In that case (assuming m>n)

m,n = A.shape
q,r = qr(A)
qhat = q[:,:n]
rhat = r[:n]

should work.

-Travis O.




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