SymPy cannot solve an equation that Matlab can
python, sympy
Solution
- Use the sympy version of Pi.
- Substitute `cos(i_)` by a new variable `ci_`, replace `sin(i_)**2` by `1-ci_**2`, and solve for `ci_`.
This should do it:
from sympy import symbols,solve,sin,cos,pi
[n_,Re_,p_,ci_,J2_,Pe_] = symbols(['n_','Re_','p_','ci_','J2_','Pe_'])
del_ss = -((3*n_*(Re_**2)*J2_/(4*(p_**2)))*(4-5*(1-ci_**2)))-((3*n_*(Re_**2)*J2_/(2*(p_**2)))*ci_)-((2*pi)/Pe_)
pprint(solve(del_ss,ci_))
(Edited because I only wrote half of the solution in the first attempt...)
Problem
I have an equation which is related to the sun-synchronous resonance condition in orbital mechanics. I'm learning Python at the moment, so I attempted to solve it in SymPy using the following code: ``` from sympy import symbols,solve [n_,Re_,p_,i_,J2_,Pe_] = symbols(['n_','Re_','p_','i_','J2_','Pe_']) del_ss = -((3*n_*(Re_**2)*J2_/(4*(p_**2)))*(4-5*(sin(i_)**2)))-((3*n_*(Re_**2)*J2_/(2*(p_**2)))*cos(i_))-((2*pi)/Pe_) pprint(solve(del_ss,i_)) ``` The expression can be successfully rearranged for five of the variables, but when the variable `i_` is used in the `solve` command (as above), an error is produced: ``` Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 479, in runfile execfile(filename, namespace) File "C:\Users\Nathan\Python\sympy_test_1.py", line 22, in <module> pprint(solve(del_ss,i_)) File "C:\Python27\lib\site-packages\sympy\solvers\solvers.py", line 484, in solve solution = _solve(f, *symbols, **flags) File "C:\Python27\lib\site-packages\sympy\solvers\solvers.py", line 700, in _solve soln = tsolve(f_num, symbol) File "C:\Python27\lib\site-packages\sympy\solvers\solvers.py", line 1143, in tsolve "(tsolve: at least one Function expected at this point") NotImplementedError: Unable to solve the equation(tsolve: at least one Function expected at this point ``` However, when the same expression is entered into Matlab and the `solve` command is called, it is rearranged correctly. I realise that the error mentions a non-implemented feature and that the two functions will no doubt differ, but it would still be nice to know if there's a more appropriate SymPy function that I can use. Any help would be greatly appreciated.