creating a multi colored graph with respect to the values in y-axis

[Ravikanth]

On Jun 15, 10:32 am, Wanderer <wande... at dialup4less.com> wrote:
> On Jun 15, 11:04 am, Ravikanth <vvnrk.vanapa... at gmail.com> wrote:
>
>
>
>
>
> > Hi all,
>
> > I am a beginner in python. I need to implement a graph with multiple
> > colors in it.
> > In a way, I have a function which varies with respect to time and
> > amplitude. I have time on x-axis and amplitude on y-axis. Lets say the
> > amplitude of the graph is divided into 4 ranges, say 1-3,3-5,5-9,
> > 10-3. I need to plot the graph in such a way that, when the values of
> > amplitude are in a particular range say 1-3, the color of graph should
> > be red.
> > If the amplitude is in the range from 3-5 the graph need to be in
> > color blue etc..,
>
> > Can somebody guide me on this, how to achive this functionality.
>
> > Regards,
> > Ravikanth
>
> Check out the examples in matplotlib.
>
> http://matplotlib.sourceforge.net/examples/pylab_examples/multicolore...- Hide quoted text -
>
> - Show quoted text -

I did go through the side wanderer.

I wasn't able to figure out the usage of boundaryNorm and
lc.set_array(z) , in that link.
according to my understanding,

cmap = ListedColormap(['r', 'g', 'b'])
norm = BoundaryNorm([-1, -0.5, 0.5, 1], cmap.N)

In the above lines of code, as per my understanding,
Listedcolor map, maps the colors r,g and b to specific indexes into
cmap
i.e cmap(0) represents red,
cmap(1) represents blue
cmap(2) represents green.
for any index greater than 3 a color of blue is returned..

>>> cmap = ListedColormap(['r', 'g', 'b'])
>>> cmap(0)
(1.0, 0.0, 0.0, 1.0)
>>> cmap(1)
(0.0, 0.5, 0.0, 1.0)
>>> cmap(2)
(0.0, 0.0, 1.0, 1.0)
>>> cmap(3)
(0.0, 0.0, 1.0, 1.0)

In this context, I was not able to understand what does boundaryNorm
does.
We have 3 colors and we are using 4 values as argument in boundaryNorm.
[-1, -0.5, 0.5, 1], the comment reads slope of 'z' is being mapped to
the values in boundary norm. How is it handled.
Does the function call " lc.set_array(z) " does it ?  what is the
exact use of linecollection.set_array(z) in this context.

Thanks,
Ravikanth