Dimensional Analysis

[XR-7 RKE]

Hey guys,

Does sympy support round a number to significant figures?

[Peter Stahlecker]

you might want to check floating point numbers in the sympy documentation.

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[Oscar Benjamin]

The ordinary Python round function can do this:

https://docs.python.org/3/library/functions.html#round

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[gu...@uwosh.edu]

An alternative interpretation of your question is that you are asking if sympy is aware of the rules for propagating significant digits through calculations? The answer is no. You have to apply the rules yourself to decide appropriate rounding.

Additional alternatives:  1) set up interval arithmetic to get a more precise version of the significant figures rules; 2) do full error propagation to determine uncertainties in your computations.

Jonathan

[Roberto Colistete Jr.]

    Not SymPy, but the Uncertainties (Python module) does what you want if you use "print(x)", where x is a ufloat number (with uncertainties).
https://pythonhosted.org/uncertainties/user_guide.html#printing

Em 17/11/2022 10:30, gu...@uwosh.edu escreveu:

[XR-7 RKE]

Yes. This exactly. Oh. sadly sympy doesn't support :'(

[Peter Stahlecker]

My limited understanding of sympy is, that it is used for symbolic calculations.

If you then want numerical calculations, is it not better to convert your sympy results to, say, numpy results ( using e.g. lambdify(..) )? Then you have the full power of numpy, scipy, etc. There is even a special library to handle calculations with floats having uncertainties. (This was mentioned earlier in this dialogue) 

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Best regards,

Peter Stahlecker

[Jeremy Monat]

Here's an example of using SymPy's lambdify() to convert a SymPy function to a numerical function that e.g. SciPy can use: Numerically Solve an ODE in SciPy

Best,

Jeremy Monat

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[S.Y. Lee]

If you expect correct decimal arithmetic and rounding, it could be better look at the alternatives like decimal library.
I don't think that there is any good unified library of combining arbitrary precision arithmetic with different rounding option yet,
but it would not be more difficult to program straightforwardly from integers, if you want to experiment with customized decimal, rounding option,
unless someone provides some encyclopedia.

[XR-7 RKE]

Thank you. Will check it out!