David, I want to make sure I understand the behavior you would prefer, because I think I can implement it in algebra-with-sympy <https://gutow.github.io/Algebra_with_Sympy/algebra_with_sympy.html>. The package already does some pre-parsing, so I think I could handle it there.
Here is what I think you are asking for: 1. Any number that is not in scientific notation and does not contain a decimal point would be considered an integer and be converted to S(). 2. All other numerical values would be treated as they normally are. Is that all you are asking for or do you need something more sophisticated? As more of these usage questions come up, I am beginning to wonder if sympy needs an interactive mode that implements sensible/useful extensions and defaults that would get in the way of sympy's use as a symbolic manipulation back-end? The idea would be to have these features only turned on in the interactive mode. Jonathan On Monday, July 3, 2023 at 7:25:00 AM UTC-5 Oscar wrote: > On Mon, 3 Jul 2023 at 00:16, David Bailey <[email protected]> wrote: > > > > On 02/07/2023 23:44, Oscar Benjamin wrote: > > > On Sun, 2 Jul 2023 at 23:06, David Bailey <[email protected]> wrote: > > >> Dear Group, > > >> > > >> If I want to enter m+1/2, I define m as a symbol and write: > > >> > > >> m+S(1)/2. > > >> > > >> However if I have a complicated expression with lots of fractions, > such as: > > >> > > >> 1 + x*(m + 1/2)/(2*m + 1) + x**2*(m + 1/2)*(m + 3/2)/(2*(2*m + > 1)*(2*m + 2)) > > >> > > >> it would be much neater if I could automatically wrap all the integers > > >> in S so that no floating point numbers get introduced. > > >> > > >> Is that feasible? I did try wrapping the whole expression in S, but > that > > >> does not work. > > > You can wrap the whole expression in nsimplify: > > > > > > >>> e = 1 + x*(m + 1/2)/(2*m + 1) + x**2*(m + 1/2)*(m + 3/2)/(2*(2*m > > > + 1)*(2*m + 2)) > > > >>> print(e) > > > x**2*(m + 0.5)*(m + 1.5)/((2*m + 2)*(4*m + 2)) + x*(m + 0.5)/(2*m + 1) > + 1 > > > >>> print(nsimplify(e)) > > > x**2*(m + 1/2)*(m + 3/2)/((2*m + 2)*(4*m + 2)) + x*(m + 1/2)/(2*m + 1) > + 1 > > > > > > The nsimplify function will attempt to guess what rational number a > > > float represents. In your example this is easy because all floats are > > > exactly represented in binary (having only twos in the denominator) > > > but otherwise the conversion can be inexact: > > > > > > >>> f = 1/3 > > > >>> f > > > 0.3333333333333333 > > > >>> print(Rational(f)) # exact value of the binary float > > > 6004799503160661/18014398509481984 > > > >>> nsimplify(f) # probably the value that the float was intended to > have > > > 1/3 > > > > > Thanks Oscar for that incredibly fast reply, but I'm not super keen on > > algebra that is only probably correct! > > Agreed but that means that you need to avoid creating floats in the > first place. Many users find it awkward to do this and prefer to use > nsimplify. > > Another option is to call S with a string:: > > In [27]: s = '1 + x*(m + 1/2)/(2*m + 1) + x**2*(m + 1/2)*(m + > 3/2)/(2*(2*m + 1)*(2*m + 2))' > > In [28]: print(S(s)) > x**2*(m + 1/2)*(m + 3/2)/((2*m + 2)*(4*m + 2)) + x*(m + 1/2)/(2*m + 1) + 1 > > -- > Oscar > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/15dc8722-b2d6-42fc-aef7-5110174d14f0n%40googlegroups.com.
