On 06/24/2010 04:03 AM, Benjamin Root wrote:
> Ah, I just noticed that.
>
> Actually, I think I just figured out what is happening. The colorbar
> automatically chooses what values to display, and in your case, the
> values are 0.0, -0.4, -0.8, -1.2, -1.6, ..., -3.6, which when turned
> into integers are 0, 0, 0, -1, -1, ..., -3, which matches what your
Right, good eye!
> first plot had. All we have to do is specify the values that the
> colorbar should list. I am not very familiar with this aspect, but it
> has something to do with specifying your colormap and/or the normalizer.
The tick locations can be specified via the ticks kwarg to colorbar.
From the docstring:
*ticks* [ None | list of ticks | Locator object ]
If None, ticks are determined automatically from the
input.
*format* [ None | format string | Formatter object ]
If None, the
:class:`~matplotlib.ticker.ScalarFormatter` is used.
If a format string is given, e.g. '%.3f', that is
used. An alternative
:class:`~matplotlib.ticker.Formatter` object may be
given instead.
The OP may also wish to specify the range of the colormap via the vmin
and vmax kwargs to pcolor (note that everything to do with the colormap
and the norm is specified in pcolor, not in the call to colorbar.
The OP probably does not need to specify both the formatter and the
ticker. If it is certain that the range of values will be substantially
geater than one, and integer tick values are desired, then try this:
int_ticker = MaxNLocator(nbins=6, integer=True)
cbar = colorbar(ticks=int_ticker)
nbins is the maximum number of intervals (one less than the max number
of ticks).
The default formatter will print integers as integers, so no custom
formatter is needed. Specifying a custom format or formatter is risky
because, as illustrated by your diagnosis of the OP's original problem,
it can easily lead to labels that are not accurate representations of
the tick values.
>
> Does anybody know of a good tutorial on creating colormaps and normalizers?
Custom norms are rare, and I don't think there is much in the way of
documentation or examples. The code in ticker.py is probably the best
starting place for learning about customizing norms; it includes
subclasses of Normalize. Colormaps are illustrated fairly well in the
examples. See the second example in
http://matplotlib.sourceforge.net/examples/pylab_examples/contourf_demo.html
for ListedColormap, see
http://matplotlib.sourceforge.net/examples/pylab_examples/contourf_demo.html
for examples of how to use the somewhat complicated
LinearSegmentedColormap to generate a custom map, and
http://matplotlib.sourceforge.net/examples/pylab_examples/show_colormaps.html
for a view of built-in colormaps.
Eric
>
> Ben Root
>
>
> On Thu, Jun 24, 2010 at 8:53 AM, Benoit Donnet
> <benoit.don...@uclouvain.be <mailto:benoit.don...@uclouvain.be>> wrote:
>
> Hello Benjamin,
>
> Thanks for your reply.
>
>> Is there any particular reason why you can't do a log10() of the
>> data that is being pcolor()'d and then label the colorbar as
>> having units of dB? That would seem to be the most
>> straight-forward approach to me.
>
> That's what I first tested.
>
> In that case, labels on the colorbar are the following (i don't
> attach the plot to avoid spamming the entire mailing-list): 0.0,
> -0.4, -0.8, -1.2, -1.6, ..., -3.6). It does not mean anything :s
>
> Benoit
>
>>
>> Ben Root
>>
>>
>> 2010/6/24 Benoit Donnet <benoit.don...@uclouvain.be
>> <mailto:benoit.don...@uclouvain.be>>
>>
>> Hi guys,
>>
>> I'm struggling with colorbar since this morning. I'd like the
>> colorbar being logscale
>>
>> I'm experimenting some strange behavior with the colorbar as
>> some 'labels' appear several times. For instance, 10^0
>> appears three times, 10^1 appears also three times, and so on.
>> I believe the exponent is the digit of the float, while I'd
>> like to see the exponent (of the scientific notation)
>>
>> I attach a png of the plot
>>
>> Here is my code:
>>
>> k,m,fp = np.loadtxt(file, unpack=True)
>> ki = linspace(k.min(), k.max(), 37)
>> mi = linspace(m.min(), m.max(), 37)
>> Z = griddata(k, m, fp, ki, mi)
>> Z.shape
>> K, M = meshgrid(ki, mi)
>>
>> pcolor(K, M, log10(Z))#, cmap=cm.gray)
>> cbar = colorbar(format=FormatStrFormatter('$10^{%d}$'))
>>
>> semilogy()
>> axis([1,20,10000,500000], font2)
>> xlabel(r'\textrm{\# hash functions ($k$)}', font)
>> ylabel(r'\textrm{vector size ($m$)}', font)
>> cbar.ax.set_ylabel(r'$f_p$', font)
>>
>> I obviously suspect my code is flawed somewhere but I can't
>> figure out where. i have tested several format for the
>> colorbar, like LogFormatterMathText, but it does not solve my
>> problem.
>>
>> I would appreciate any kind of help. Thanks in advance
>>
>> Keep on Rockin'
>>
>> Benoit
>>
>>
>>
>>
>> ---
>> Dr. Benoit Donnet
>> Université catholique de Louvain (UCL)
>> Ecole Polytechnique de Louvain (EPL) - Département
>> d'Ingénierie Informatique (INGI)
>> Place Sainte Barbe, 2
>> B-1348 Louvain-la-Neuve
>> Phone: +32 10 47 87 18
>> Fax: +32 10 45 03 45
>>
>>
>>
>>
>>
>>
>>
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>
> ---
> Dr. Benoit Donnet
> Université catholique de Louvain (UCL)
> Ecole Polytechnique de Louvain (EPL) - Département d'Ingénierie
> Informatique (INGI)
> Place Sainte Barbe, 2
> B-1348 Louvain-la-Neuve
> Phone: +32 10 47 87 18
> Fax: +32 10 45 03 45
>
>
>
>
>
>
>
>
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