#20026: Reverse the scale of colors in Matrix.plot
-------------------------+-------------------------------------------------
Reporter: | Owner:
ncohen | Status: needs_info
Type: | Milestone: sage-7.1
enhancement | Resolution:
Priority: major | Merged in:
Component: | Reviewers: Jori Mäntysalo
linear algebra | Work issues:
Keywords: | Commit:
Authors: | 791fe5552026c199a7ce575bc594a8e705972549
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
public/20026 |
Dependencies: |
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Comment (by kcrisman):
Ok, here is a question. What should we expect about these?
{{{
sage: matrix([[0,0,],[1,1]]).plot()
sage: matrix([[-1,-1],[1,1]]).plot()
sage: matrix([[-10,-10],[0,0]]).plot()
sage: matrix([[0,0],[0,0]]).plot()
sage: matrix([[-100,0],[100,0]]).plot()
}}}
As to modifying documentation, I think it would be good to be more
specific about the default here (writing for the current)
{{{
If the matrix is dense, each matrix element is given a different
color value depending on its relative size compared to the other
elements in the matrix.
+ The default is for the lowest number to be black and the highest
+ number to be white in a greyscale pattern; see the information about
+ normalizing below.
}}}
One could add
{{{
+ To achieve the lowest number to be white and the highest black, use
+ `cmap='Greys'` (see below for syntax).
}}}
or whatever is appropriate. Similarly, with the sparse matrices it would
be super-helpful to say why the "unexpected" is done - compatibility with
matplotlib/matlab.
I can document whatever we do once we agree on something, since it appears
that no one on sage-devel cares about this, so hopefully we can find a
consensus here. But I am not really sure there is an "obvious" answer for
the last matrix. See also the `norm` and `vmin` and `vmax`, e.g.
{{{
sage: matrix([[-100,0],[100,0]]).plot(norm='value')
<three black squares, currently>
}}}
Or even compare
{{{
sage: matrix([[-10,0],[0,10]],sparse=True).plot()
sage: matrix([[-10,0],[0,10]],sparse=False).plot() # current default
sage: matrix([[-10,0],[0,10]],sparse=False).plot(cmap='Greys') # your
suggestion
}}}
So I'm not really sure what to do about this, as the whole point of a
scale is that it goes negative to positive.
{{{
sage: identity_matrix(10).plot() # agreed, not ideal
sage: (-1*identity_matrix(10)).plot() # ?!#$$!
}}}
There is a fundamental discord between wanting things to behave like the
sparse where zero is white, and wanting to be able to do a whole range
from negative to positive.
----
Also annoying but probably not worth doing on this ticket: `matrix_plot?`
is helpful but `matrix().plot?` is not.
--
Ticket URL: <http://trac.sagemath.org/ticket/20026#comment:20>
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