[Numpy-discussion] another matrix operation

josef.pktd@gmai... josef.pktd@gmai...
Mon Mar 15 09:14:47 CDT 2010


On Mon, Mar 15, 2010 at 9:09 AM, Gerardo Berbeglia <gberbeglia@gmail.com> wrote:
> I would like to do with numpy the following operation.
>
> Let A be an n x n matrix and let s be an integer between 1 and n.
>
> I would like to have an n x n matrix B = f(A,s) such that
>
> - If we only look at the first s columns of B, we will not see any
> difference with respect to the first s columns of the n x n identity
> matrix.
>
> - For the last n-s columns of B, we will not see any difference with
> respect to the last n-s columns of A.
>
> Example. n = 4, s = 2
>
> A= [[2,2,2,2],[3,3,3,3],[4,4,4,4],[5,5,5,5]]
>
> B= f(A,s) = [[1,0,2,2],[0,1,3,3],[0,0,4,4],[0,0,5,5]]
>
> Is there a way to do this efficiently (without loops)?

something like this ?

B = A.copy()
B[:s,:] = np.eye[:s,:]

Josef

>
> Thanks in advance.
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