Now I see a solution: forget the function and create the expression exp
using string manipulation and exec, something like
strExp = 'complex string'
strSym = 'exp = ' + strExp
exec(strSym)
On Wednesday, November 4, 2020 at 9:51:35 AM UTC+1 Thomas Ligon wrote:
> Thanks!
> The automatic subscript is just a minor irritation, and your response is
> helpful.
> I have included a new test program that hopefully no longer oversimplifies
> the situation. Currently, I have code (2000 lines) for investigating a very
> complex series, and it runs to a maximum of 3 terms of the series,
> requiring index values up to 6. I showed the results to the mathematics
> professor who has mentored my work and he immediately says that it is
> valuable and I should publish a version that can go up to a very large
> number of terms. In order to do that, I need to produce a fully automated
> version with a variable number of terms and indices.
> So, for variable j, I want to use a_j in a formula.
> The expression exp on line 20 does that, where I use get_a(1) to represent
> aj for variable j, where j happens to be 1.
> In line 5, the return is part of a function. In line 8, I expect return in
> exec ('return...') to be a part of a function.
>
> maxIndex = 2
> import sympy
> from sympy import symbols, latex
> def get_a1():
> return a1
> def get_a2():
> strSym = 'return a2'
> exec(strSym)
> def get_a (j):
> strSym = 'return a' + str(j)
> exec(strSym)
> lam = symbols('\\lambda')
> for ind in range(1,maxIndex+1):
> strSym = 'a' + str(ind) + ' = symbols(\'a_' + str(ind) + '\')'
> exec(strSym)
> #a1 = symbols('a_1')
> #a2 = symbols('a_2')
> print(latex(get_a1()))
> #print(latex(get_a2())) # causes 'return' outside function (<string>, line
> 1)
> exp = 3*get_a(1) + 5*get_a(2)*lam**2 # causes 'return' outside function
> (<string>, line 1)
> print(latex(exp))
> print('end testSym')
>
> On Tuesday, November 3, 2020 at 11:29:00 PM UTC+1 [email protected] wrote:
>
>> I'm unclear what you're trying to achieve with the functions. exec()
>> takes a string of Python code and executes it. The entire string must
>> be valid Python code by itself, so exec('return x') fails because a
>> bare "return x" is not valid Python. "return" must be inside a
>> function definition to be valid. But even defSym1 doesn't do anything
>> useful beyond just returning Sym1, so there's no point to having it
>> instead of just "Sym1" directly.
>>
>> The LaTeX version of Sym1 contains _ because SymPy automatically
>> assumes that symbol names ending in numbers are subscripted, so it
>> renders it as a Sym_1 in LaTeX. If you don't want the 1 to be
>> subscripted, you can use something like Symbol("{Sym1}").
>>
>> Aaron Meurer
>>
>> On Tue, Nov 3, 2020 at 9:42 AM Thomas Ligon <[email protected]> wrote:
>> >
>> > The following code is not working as I expected.
>> > Why does Sym1 contain an underline (_{1})?
>> > Why does return fail (unhandled exception) in line 7?
>> >
>> > Code:
>> > import sympy
>> > from sympy import symbols, latex
>> > def defSym1():
>> > return Sym1
>> > def defSym2():
>> > strSym = 'return Sym2'
>> > exec(strSym)
>> > Sym1 = symbols('Sym1')
>> > Sym2 = symbols('Sym2')
>> > print(latex(defSym1()))
>> > print(latex(defSym2()))
>> > print('end testSym')
>> >
>> > Output:
>> > Sym_{1}
>> > 'return' outside function (<string>, line 1)
>> >
>> >
>> >
>> >
>> > --
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>>
>>
>>
>
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