matplotlib-users Mailing List for matplotlib

Uwe Schmitt wrote:
> Hi,
> 
> I would like to plot contours with a nonlinear mapping from values to 
> color as follows:
> 
>    -1  ->  red
>     0  ->  white or green or black
>    +1  ->  red
> 
> How can I achieve this ?

See examples/contourf_demo.py.  The relevant part is this:

# Now make a contour plot with the levels specified,
# and with the colormap generated automatically from a list
# of colors.
levels = [-2, -1.5, -1, -0.5, 0, 0.5, 1, 1.5]
CS3 = contourf(X, Y, Z, levels,
                         colors = ('r', 'g', 'b'),
                         origin=origin)

Try specifying 4 levels; I think this would do what you want (with black 
for the middle range, for example):

levels = [-1.5, -0.5, 0.5, 1.5]
CS = contourf(X, Y, Z, levels, colors=('r', 'k', 'r'))

Eric


> 
> Greetings, Uwe
>    
> 
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John Pye wrote:
> Hi Eric
> 
> I tried the new spy function under Windows and it seemed to work OK. A
> great leap forward, actually, given the problems I had been seeing.
> Merging the spy functions was a good idea (does it work ok for very very
> large, very sparse matrices?)

I don't know any reason it would not, but I have not tried it.

> 
> Trying it under Ubuntu was less straightforward. I built an RPM (python
> setup.py bdist_rpm) then converted it to deb package then installed it.
> It complained about my old ~/.matplotlib/matplotlibrc file so I moved it
> out of the way. Then I fired up again and it was OK.

That sounds like the hard way.  I find it easy to build and install 
directly from source--from svn in my case, but from a tarball should be 
the same.  I install it in /usr/local instead of /usr/ so as to keep the 
distinction between things installed as packages and custom installations.

> 
> In my new Ubuntu install of matplotlib, sans matplotlibrc, I would like
> to switch GUIs to GTKAgg but there doesn't seem to be a
> /etc/matplotlibrc file from which to base my configuration. Is this a
> fault of my rpm-to-deb process, or something that failed during build?
> Is it still possible to run the GTKAgg GUI? Has the config system changed?

A system-wide matplotlibrc file should get installed somewhere--try 
using "locate" to find it.  I think a change was made since 0.90 such 
that yours will be in a different place than mine is now.  If it turns 
out that it got lost in the rpm-to-deb conversion, then look at 
matplotlibrc.template in the source directory.  With a couple of string 
substitutions you can manually turn that into a valid matplotlibrc file 
and specify your numerix (numpy, I hope) and backend.  You can always 
put it in your ~/.matplotlib directory, and make local copies in working 
directories if you want different defaults for a given project.

> 
> Finally, can I suggest that the website be updated with some information
> about the new release? I couldn't find any readable information about it
> on-line -- had to go to the tarball. I think generally the matplotlib
> community would benefit from more frequently updated website. While I'm
> at it, maybe I could suggest a matplotlib wiki that gets a bit more
> prominance on the homepage and that is *separate* from the scipy one,
> since the scipy wiki gives completely mixed messages about what plotting
> engine is preferred (chaco.wx and VTK and so on) -- it can't be helping
> the matplotlib cause.
> http://matplotlib.sourceforge.net/whats_new.html (bit out of date)

Thanks for the good suggestions.  I agree that there could be 
improvements--it is just a question of who can find the time and 
motivation to make them, amid competing pressures.

Eric


> 
> Cheers
> JP

If one inserts a colorbar after using matshow, then the matrix plot's 
aspect ratio is incorrect altered.  Here are 2 cases to compare

import pylab
matrix = pylab.rand(30,30)

1) matshow() before colorbar()

pylab.matshow(matrix)
pylab.colorbar()
pylab.show()

The matrix plot is squished in the x-direction while not in the y thus 
losing its proper aspect ratio (equal by default).

2) imshow() before colorbar()

pylab.imshow(matrix)
pylab.colorbar()
pylab.show()

Everthing is okay in this case.


Thanks,
Suresh

Uwe,

I don't know the answer to your question, but yesterday Rob Hetland  
sent out and email entitled "Creating a non-linear colormap." that  
includes example code.  That might help you get started.

Ken

Hi,

I would like to plot contours with a nonlinear mapping from values to 
color as follows:

   -1  ->  red
    0  ->  white or green or black
   +1  ->  red

How can I achieve this ?

Greetings, Uwe
   

Hi, I have a problem. The following script crashes:

    from pylab import *

    a=arange(1500).reshape(50,30)

    figure()
    figimage(a)

    show()

Python says:

  Traceback (most recent call last):
  File "crash.py", line 5, in ?
    figimage(a)
  File "c:\Python24\lib\site-packages\matplotlib\pylab.py", line 810, in 
figimage
    draw_if_interactive()
  File 
"c:\Python24\lib\site-packages\matplotlib\backends\backend_tkagg.py", 
line 59, in draw_if_interactive
    figManager.show()
  File 
"c:\Python24\lib\site-packages\matplotlib\backends\backend_tkagg.py", 
line 301, in show
    self.canvas.draw()
  File 
"c:\Python24\lib\site-packages\matplotlib\backends\backend_tkagg.py", 
line 151, in draw
    FigureCanvasAgg.draw(self)
  File 
"c:\Python24\lib\site-packages\matplotlib\backends\backend_agg.py", line 
398, in draw
    self.figure.draw(renderer)
  File "c:\Python24\lib\site-packages\matplotlib\figure.py", line 515, 
in draw
    im.draw(renderer)
  File "c:\Python24\lib\site-packages\matplotlib\image.py", line 473, in 
draw
    renderer.draw_image(self.ox, self.oy, im, self.origin, self.figure.bbox)
    IndexError: Unexpected SeqBase<T> length.

    This application has requested the Runtime to terminate it in an 
unusual way.
    Please contact the application's support team for more information. 

As you can see, I'm using Python 2.4. Matplotlib is from the Enthought 
Python Edition,
version number is 0.87.2. I tried Google, but looking for "Unexpected 
SeqBase matplotlib" did not help me.

Any hints ?

Greetings, Uwe

Dear all:

I am trying the numpy-scipy-matplotlib stack on Opensuse 10.2 from

  http://repos.opensuse.org/science/openSUSE_10.2/i586/

No success with matplotlib, however.  Two problems:

- No plot windows open at all

- When using TeX ouput, ghostscript segfaults:

  sh: line 1: 11319 Segmentation fault      gs -dBATCH -dNOPAUSE -r6000 -sDEVICE=pswrite -sPAPERSIZE=letter -sOutputFile="/tmp/ef684d47fbac423478eccceef602c8ca.ps" "/tmp/ef684d47fbac423478eccceef602c8ca" >"/tmp/ef684d47fbac423478eccceef602c8ca.output"

So in short, nothing works.  Has anybody been successfully running
this RPM?  (Background: This is for the teaching lab computers at my
university where I'd like to experiment with in-class use of scipy.  I
have an agreement with the sysadmin that he'd install
numpy-scipy-matplotlib if it runs "out-of-the-box" from a standard
repository without any manual fiddling.  Otherwise, I'd be out of
luck.  On my personal workstation I run Fedora where I never had any
problem with the "official" RPMs from Fedora Extra...)

Regards,
Marcel

PS.: Yes, I got past the BLAS/Lapack problem.  Short answer: Don't use
the official blas and lapack packages from Suse, they are incomplete.
Use the RPMs from the repository above.

hello, I have an application I'm working on, and I need to remove figtext() without using a figure.clear(). how can I do this? thanks.
   
  Jeff

 
---------------------------------
The fish are biting.
 Get more visitors on your site using Yahoo! Search Marketing.

Hi Eric

I tried the new spy function under Windows and it seemed to work OK. A
great leap forward, actually, given the problems I had been seeing.
Merging the spy functions was a good idea (does it work ok for very very
large, very sparse matrices?)

Trying it under Ubuntu was less straightforward. I built an RPM (python
setup.py bdist_rpm) then converted it to deb package then installed it.
It complained about my old ~/.matplotlib/matplotlibrc file so I moved it
out of the way. Then I fired up again and it was OK.

In my new Ubuntu install of matplotlib, sans matplotlibrc, I would like
to switch GUIs to GTKAgg but there doesn't seem to be a
/etc/matplotlibrc file from which to base my configuration. Is this a
fault of my rpm-to-deb process, or something that failed during build?
Is it still possible to run the GTKAgg GUI? Has the config system changed?

Finally, can I suggest that the website be updated with some information
about the new release? I couldn't find any readable information about it
on-line -- had to go to the tarball. I think generally the matplotlib
community would benefit from more frequently updated website. While I'm
at it, maybe I could suggest a matplotlib wiki that gets a bit more
prominance on the homepage and that is *separate* from the scipy one,
since the scipy wiki gives completely mixed messages about what plotting
engine is preferred (chaco.wx and VTK and so on) -- it can't be helping
the matplotlib cause.
http://matplotlib.sourceforge.net/whats_new.html (bit out of date)

Cheers
JP

Eric Firing wrote:

> > John Pye wrote:
>   
>> >> Hi all
>> >>
>> >> I have got some funny behaviour here that looks like a bug with the
>> >> spy() function. Using the latest python-matplotlib 0.87.5 package on
>> >> Ubuntu 6.10, I try:
>> >>
>> >> $ ipython -pylab
>> >> from scipy import io
>> >> M = io.mmread('gd.mm')
>> >> spy(M)
>> >> M.shape
>> >> M.nnz
>> >>
>> >> It looks great and I get the necessary number of dots on my 'spy' plot.
>> >> Then:
>> >>
>> >> spy(M.todense())
>> >>
>> >> This seems to plot only half of the points. At first I thought the
>> >> 'todense' function must be to blame, however:
>> >>
>> >> D = M.todense()
>> >> for i in range(0,231):
>> >>     for j in range(0,231):
>> >>         if D[i,j]:
>> >>             print i,j,D[i,j]
>> >>
>> >> gave me the right data, so it really looks like a bug with spy().
>> >>
>> >> And FWIW spy2(M) fails with an error, whereas spy2(D) shows the same bug
>> >> as spy(D).
>> >>
>> >> Is this something that has been fixed in the new 0.90 release?
>>     
> >
> > The two versions of spy were merged into one, with some rewriting, in
> > 0.90.  Please give it a try and see if the problem persists.
> >
> > Eric
>