On Fri, Aug 31, 2018 at 11:15 AM, John H Palmieri
<[email protected]> wrote:
> The question
>
>
> https://ask.sagemath.org/question/43517/conflicting-sage-vs-wolfram-evaluation-of-a-limit/
>
> brought the following question to mind: can you specify the precision to
> which a function is evaluated when plotting it? The particular
> ask.sagemath.org question involves a function which has "inherent numerical
> instability", as kcrisman says in his answer. For example, evaluating V(20,
> 1).n() will result in "ValueError: power::eval(): division by zero", but
> V(20,1).n(300) gives an actual number. Is there a way to pass the numerical
> precision to the plot function?
>
> (I am not an expert in the plotting code in Sage, but when I look at the
> plot code, I see the function "generate_plot_points" which calls
> float(f(...)). That makes me think that the available precision is fixed.
> But maybe I'm wrong.)
I wrote a lot of the plot code and I think it only works with floats.
I don't think we implemented anything at all to automatically deal
with high precision.
As a workaround, if you have a function f you want to plot to high
precision, maybe do this:
R = RealField(500)
def wrap(x):
# x is a floating point number
return f(R(x))
plot(wrap, ...)
---
Alternatively, compute in any way you want (to very high precision) a
list v of pairs (x,y), then do "line(v)" to get a plot of that.
>
> --
> John
>
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--
William (http://wstein.org)
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