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I have been using BSplineFunction (Mathematica 8) to generate a smooth representation of some data, which I might then do some further processing on.

As I understand it, BSplineFunction should be analytic and I should be able to pull out a value anywhere. The results of BSplineFunction however are limited to MachinePrecision, regardless of the input data's precision or accuracy. For example,

data = {{17980, -1}, {17990, -1}, {18000, 0}, {18010, 1}, {18020, 
3}, {18040, 0}, {18050, -1}, {18080, 2}, {18100, 0}};

f = BSplineFunction[data, SplineDegree -> 3];

Asking for a value:


Will give

{18001.6, 0.158667}

Initially, I thought something like


would produce an answer with 300 digits for example, but instead it only returns the same answer as above.In fact, changing the 300 to 3 also produces the same result.

Note, Precision[data] and Accuracy[data] both give $\infty$. However, Precision[f], and Accuracy[f] give MachinePrecision, and 14.9546, respectivley.

PrecisionGoal and AccuracyGoal are not available options for BSplineFunction (it lets you know if you try). It will take setting WorkingPrecision to some number as an option, for example,

f = BSplineFunction[data, SplineDegree -> 3, WorkingPrecision -> 8000]

without giving any error, but the answers remain unchanged.

Am I trying to get answers out of BSplineFunction it simply isn't possible for it to give, or is there perhaps some other setting I need to explore?

Thank you for any assistance.

share|improve this question
This came up recently and no one had a suggestion for precise or arbitrary precision output. I'm not saying it cannot be done however. +1 on the question. –  Mr.Wizard Aug 1 '13 at 0:17

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