Update: An angel on GitHub told me that I can overcome this problem by
using solveset() instead of solve().
But why does solve() not work as expected?
On Tuesday, December 10, 2019 at 12:41:46 PM UTC-5, Damon Turney wrote:
>
> Hi Forum,
>
> Help! sympy.solve() always uses precision of 15 no matter what I try.
>
> Recreated problem results:
>
> In [*164*]: *import* *sympy*
>
>
>
> In [*165*]: w,x,y,z=sympy.symbols('w,x,y,z')
>
>
>
> In [*166*]:
> eqn=sympy.Eq(sympy.Float('1/55500',45)*w,sympy.Float('96500.0')*y)
>
>
>
> In [*167*]: eqn.evalf(45)
>
>
>
> Out[*167*]: Eq(0.000018018018018018018018018018018018018018018018*w,
> 96500.0*y)
>
> In [*168*]: sympy.solve(eqn,y)[0].evalf(45)
>
>
>
> Out[*168*]: 0.000000000186715212621948369903318027445619613213789734*w
>
> In [*169*]: sympy.solve(eqn.evalf(45),y)[0].evalf(45)
>
>
>
> Out[*169*]: 0.000000000186715212621948369903318027445619613213789734*w
>
> The more accurate coefficient (to 45 digit accuracy) is:
>
> In [*152*]: sympy.Float('1/55500',45)/sympy.Float('96500.0',45).evalf(45)
>
>
>
> Out[*152*]: 0.000000000186715212621948373243710031274798114176352518
>
> In [*174*]: sympy.Float('1',45)/sympy.Float('55500',45)/sympy.Float(
> '96500.0',45).evalf(45)
>
>
> Out[*174*]: 0.000000000186715212621948373243710031274798114176352518
>
>
> So you see, the coefficient that results from sympy.solve:
>
> 0.000000000186715212621948369903318027445619613213789734
>
> is accurate to only 15 digits of precision.
>
>
> Clearly sympy.solve is using only 15 digit precision, even though I'm
> specifying 45 digit precision.
>
> How can I force sympy.solve to use 45 digit precision when it solves for
> y?
>
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