Re: [Numpy-discussion] offset in fill diagonal

2017-01-21 Thread Ian Henriksen 
On Sat, Jan 21, 2017 at 9:23 AM Julian Taylor 
wrote:

> On 21.01.2017 16:10, josef.p...@gmail.com wrote:
> > Is there a simple way to fill in diagonal elements in an array for other
> > than main diagonal?
> >
> > As far as I can see, the diagxxx functions that have offset can only
> > read and not inplace modify, and the functions for modifying don't have
> > offset and only allow changing the main diagonal.
> >
> > Usecase: creating banded matrices (2-D arrays) similar to toeplitz.
> >
>
> you can construct index arrays or boolean masks to index using the
> np.tri* functions.
> e.g.
>
> a = np.arange(5*5).reshape(5,5)
> band = np.tri(5, 5, 1, dtype=np.bool) & ~np.tri(5, 5, -2, dtype=np.bool)
> a[band] = -1
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You can slice the array you're filling before passing it to fill_diagonal.
For example:

import numpy as np
a = np.zeros((4, 4))
b = np.ones(3)
np.fill_diagonal(a[1:], b)
np.fill_diagonal(a[:,1:], -b)

yields

array([[ 0., -1.,  0.,  0.],
   [ 1.,  0., -1.,  0.],
   [ 0.,  1.,  0., -1.],
   [ 0.,  0.,  1.,  0.]])

Hope this helps,

Ian Henriksen
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Re: [Numpy-discussion] offset in fill diagonal

2017-01-21 Thread Julian Taylor 
On 21.01.2017 16:10, josef.p...@gmail.com wrote:
> Is there a simple way to fill in diagonal elements in an array for other
> than main diagonal?
> 
> As far as I can see, the diagxxx functions that have offset can only
> read and not inplace modify, and the functions for modifying don't have
> offset and only allow changing the main diagonal.
> 
> Usecase: creating banded matrices (2-D arrays) similar to toeplitz.
> 

you can construct index arrays or boolean masks to index using the
np.tri* functions.
e.g.

a = np.arange(5*5).reshape(5,5)
band = np.tri(5, 5, 1, dtype=np.bool) & ~np.tri(5, 5, -2, dtype=np.bool)
a[band] = -1
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[Numpy-discussion] offset in fill diagonal

2017-01-21 Thread josef . pktd 
Is there a simple way to fill in diagonal elements in an array for other
than main diagonal?

As far as I can see, the diagxxx functions that have offset can only read
and not inplace modify, and the functions for modifying don't have offset
and only allow changing the main diagonal.

Usecase: creating banded matrices (2-D arrays) similar to toeplitz.


Josef
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