Robert Bradshaw wrote:
> On Nov 10, 2009, at 11:25 PM, Jonathan Bober wrote:
>
>> Does anyone know how to plot a matrix so that each pixel in the output
>> picture corresponds precisely to an entry in the matrix?
>>
>> To see the problem that I have, you might see the odd results that
>> occur
>> when you do:
>>
>> M = zero_matrix(GF(2), 1000)
>> sage: M
>> 1000 x 1000 dense matrix over Finite Field of size 2
>> sage: for n in range(1000):
>> ....: for m in range(1000):
>> ....: if (n + m) % 2 == 0:
>> ....: M[n,m] = 1
>> ....:
>> sage: M
>> sage: plot(M).show(figsize=[5,5])
>> sage: plot(M).show(figsize=[6,6]) # <-- This one in particular might
>> be very surprising.
>> sage: plot(M).show(figsize=[7,7])
>>
>> I'm pretty sure that I understand why these problems occur, and I'm
>> not
>> sure if there is any good way to fix them.
>>
>> What I would like to be able to do is be able to take the above matrix
>> and produce an image with alternating black and white pixels, for
>> example. Is this possible? I'm not particularly concerned about the
>> border, or labels for the matrix, right now. I just want the picture
>> of
>> the matrix itself to look right.
>
> For matrices over F_2 you can do
>
> sage: from sage.matrix.matrix_mod2_dense import to_png
> sage: to_png(M, "M.png")
>
> Otherwise, I'm not sure how to do this, as it uses the numpy
> _render_on_subplot method which does its own interpolation. (This is
> also an issue with contour and complex plots, where the lack of pixel
> <-> point relationship makes for fuzzier plots.)
You could use PIL for this:
sage: from PIL import Image
sage: im=Image.new('1',(1000,1000),None)
sage: im.putdata(M.list())
sage: im.save('test.png')
Now open up test.png
Thanks,
Jason
--
Jason Grout
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