Re: [Matplotlib-users] plot color as a function of values?

[Xavier G. <xav...@gm...>]

Eric Firing wrote:
> Xavier Gnata wrote:
>> Hi,
>>
>> Imagine you have something like:
>>
>> from pylab import *
>> t = arange(0.0, 2.0, 0.01)
>> s = sin(2*pi*t)
>> ax = subplot(111)
>> ax.plot(t, s)
>>
>> That's fine but now I would like to plot the negative parts of the 
>> curve in red and the positive one in green.
>> Is there a nice pylab oriented way to do that? Some kind of 
>> "conditional formating"?
>
> Not built in, but you can do it easily with masked arrays.  See 
> http://matplotlib.sourceforge.net/examples/pylab_examples/masked_demo.html 
>
>
> It is not exactly what you want, but close:
>
> sneg = np.ma.masked_greater_equal(s, 0)
> spos = np.ma.masked_less_equal(s, 0)
> ax.plot(t, spos, 'g')
> ax.plot(t, sneg, 'r')
>
> What this does not do is ensure that there is no gap where the line 
> crosses zero.  For that, you would need to ensure that your sampling 
> of s(t) includes the zeros.
>
> Eric

It should do the trick because my sampling is very high.

Xavier