Hi Roshan,
Thanks for looking at this. Just as a note to anyone interested in
this there has already been some discussion on the issue tracker:
https://github.com/sympy/sympy/issues/20071
Oscar
On Fri, 18 Sep 2020 at 13:00, Roshan VS wrote:
>
> Before I begin I would like to introduce myself, I'm Roshan (my username's
> weakit everywhere), and programming is a hobby of mine. I might not be as
> experienced as the average sympy programmer, and I'm still learning the
> ropes, so please be patient with me.
>
> The idea of a CAS is something I find very interesting, and that's why I
> would like to learn how a CAS would work, and along with that, I think I can
> gain a lot of experience helping out with sympy.
>
> Anyways, coming to my issue:
>
> Currently, when two numbers of different precision are used in an arithmetic
> operation, the result is returned with the higher precision of the two Floats:
>
> >>> Float(0.1, 3) * Float(3.1415, 5)
> 0.31417
>
> I'm looking to change this behaviour so that the result is in the lower of
> the two precisions, to have a more accurate result.
>
> I did notice this in the documentation:
>
> The precision of a number determines 1) the precision to use when performing
> arithmetic with the number, and 2) the number of digits to display when
> printing the number. When two numbers with different precision are used
> together in an arithmetic operation, the higher of the precisions is used for
> the result."
>
> So the displayed precision should not be used as a model of error propagation
> or significance arithmetic; rather, this scheme is employed to ensure
> stability of numerical algorithms.
>
> over here:
> https://docs.sympy.org/latest/modules/evalf.html#floating-point-numbers
>
> "this scheme is employed to ensure stability of numerical algorithms" is what
> I'm focusing on. Would the change I proposed break anything, or cause any
> un-stability?
>
> It's a rather simple fix, and all tests other than a few expected document
> and example tests pass.
>
> Is there something I'm missing, and also anything against this proposal? This
> is how I think Floats should behave, but I would also like to hear about any
> problems that this might create.
>
> Thanks for your time.
>
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