The documentation for plot() says:
The actual sample points are slightly randomized, so the above
plots may look slightly different each time you draw them.
I assume that this an easy way to get the behavior:
Note that this function does NOT simply sample equally spaced
points between xmin and xmax. Instead it computes equally spaced
points and add small perturbations to them. This reduces the
possibility of, e.g., sampling sin only at multiples of 2pi,
which would yield a very misleading graph.
So, perhaps this is a "feature". But it seems to me that the endpoints,
at least, should be always included (if possible) when graphing a
function, so maybe this is a bug. (Although it is nice to not include
the endpoints when plotting something like sin(1/x).)
But anyway, I think that you should be able to instead do:
f = x*sin(x^2)
v = []
graph = plot(f, [-1, 3], thickness = 1, rgbcolor = (1, 0 ,0))
for i in srange(50):
v.append(graph)
curve = animate(v)
curve.show()
On Wed, 2008-02-20 at 16:01 -0600, Jason Grout wrote:
> dean moore wrote:
> > I ran the code now living at < https://www.sagenb.org/home/pub/1691/ >,
> > but the function's graph
> > "wiggles," most notably by the right endpoint. Tested, both Firefox &
> > Internet Explorer. Same thing.
> > Read through <
> > http://www.sagemath.org/doc/html/ref/module-sage.plot.plot.html >, but
> > found nothing.
> >
> > I am animating a graph, so it appears in all frames.
> >
> > I fiddled a good deal, but was left wondering, "Is it weirdness with
> > SAGE, or my bad coding?" I beat
> > the problem to a snippet:
> >
> > /f = x*sin(x^2)
> > v = []
> > for i in srange(50):
> > graph = plot(f, [-1, 3], thickness = 1, rgbcolor = (1, 0 ,0),
> > plot_points = 1000)
> > v.append(graph)
> > curve = animate(v)/
> > /curve.show()
> >
>
> Wow, this is a great animation. Sorry the plotting is so distracting at
> the ends!
>
> To narrow down the issue, I executed the following after the code you gave:
>
> sage: endpoints = [v[i][0].xdata[-1] for i in srange(50)]
> sage: max(endpoints) - min(endpoints)
> 0.0039542538407206784
>
> This computes the endpoints for the x-values that are sampled to plot
> the graph. That's quite a spread for having the exact same inputs,
> which explains the noticable wiggling.
>
> So now the question is: why in the world do we have such different
> endpoints?
>
> I might point out that the wiggling is not just at the endpoints of the
> graph. The wiggling is throughout the graph; it's just really
> noticeable at the endpoints.
>
> Jason
>
>
>
> >
>
>
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