On Sun, 5 Mar 2023 at 08:32, Thomas Ligon <[email protected]> wrote:
>
> I have a lot of power series that look like this (but going up to t**12):
> exp1 = -2867.70035529489*t**5 + 147.938724526848*t**3 - 2.56500070531002*t
> While trying to gain some insight into the mathematics that creates them, I
> want to print a shorter version, such as
> - 2.565 t + 147.93872 t**3- 2867.70036 t**5
> but the best I have achieved is
> - 2867.70036 t^{5} + \left(147.93872 t^{3} - 2.565 t\right)
> Rounding the numbers was easy, but I would prefer to round to 5 digits total,
> not 5 digits after the decimal point. I was able to convert the expression to
> a list and sort the list, but when I converted the list back to an
> expression, I didn't succeed in producing the order I wanted.
You can get 5 digits by using exp1.evalf(5).
It is surprisingly difficult to control the order of terms in sympy's
printing functionality but it is possible:
In [1]: exp1 = -2867.70035529489*t**5 + 147.938724526848*t**3 -
2.56500070531002*t
In [2]: doprint = StrPrinter(settings={'order':'none'}).doprint
In [3]: series = Add(*sorted(exp1.evalf(5).args, key=degree), evaluate=False)
In [4]: print(doprint(series))
-2.565*t + 147.94*t**3 - 2867.7*t**5
There are two steps to controlling the order:
- Ordering the terms in the expression itself (the series variable above).
- Getting the printer to respect that ordering ('order':'none').
It should be possible to set order=None with init_printing and that
does work for the pretty printer but not for string printing (i.e.
print(expr) or str(expr)).
--
Oscar
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