Hi,
On Fri, 17 Feb 2006, Markus Meyer wrote:
> Hi everyone,
>
> I'm trying to draw graphs with discontinuities in it, like this:
>
> from pyx import *
> from math import cos, pi
>
> def f(x):
> return cos(x % (pi/2))
>
> g = graph.graphxy(width=8, height=3.25, xpos=0, ypos=8, x2=None, y2=None,
> x=graph.axis.lin(min=0, max=5, title="$t [s]$"),
> y=graph.axis.lin(min=-0.3, max=1.3, title="$U(t) [V]$"))
> g.plot(graph.data.function("y(x)=f(x)", context=locals()),
> [graph.style.line()])
> g.writePDFfile("discont")
>
> However, there are two problems with this:
>
> 1. The vertical slopes between the single instances of the sawtooths are
> not perfectly vertical. In cases, where I want to explicitely visualize
> that a function has discontinuities, this is something that will
> probably make the reader stumble.
>
> 2. In most books, the vertical slopes are not displayed at all. I cannot
> currently do this with graph.data.function.
>
> When using a graph.data.paramfunction, it looks a bit better, but when
> zooming in, one can still see, that the slopes are not perfectly
> vertical. I know that I can use graph.data.list to exactly control the
> points that are output, but I guess there should be a better way?
I think you will have to split the plotting into parts, e.g.,
if you have Numeric or numpy or numarray installed, you could do
#################################################
from pyx import *
from math import pi
from Numeric import arange, cos
npts = 100
x = pi/2.0*arange(npts)/(npts-1)
y = cos(x)
g = graph.graphxy(width=8, height=3.25, xpos=0, ypos=8, x2=None, y2=None,
x=graph.axis.lin(min=0, max=5, title="$t [s]$"),
y=graph.axis.lin(min=-0.3, max=1.3, title="$U(t) [V]$"))
for i in xrange(4):
g.plot(graph.data.list(zip(x+i*pi/2.0, y), x=1, y=2),
[graph.style.line()])
g.writePDFfile("discont")
##################################################
Of course you can construct x and y as lists, but then
adding i*pi/2.0 won't work.
Best, Arnd
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