On Jul 18, 5:44 pm, Aaron Meurer <[email protected]> wrote:
> SymPy is built on top of Python, so symbol names have to be defined to
> be used.
>
> x = Symbol('x') is no different (from Python's point of view) from x =
> 1 or x = 'x'. It is just a variable assignment. In particular, this
> means that variable names don't have to match at all the name of the
> Symbol that they hold. Nowhere can anything tell what the name of
> your variable is, or if you even used one at all (e.g., it's
> impossible for a function like solve() to tell if you used x =
> Symbol('x'); solve(x**2 - 1) or just solve(Symbol('x')**2 - 1) or even
> y = Symbol('x'); solve(y**2 - 1); they all appear exactly the same to
> it).
>
> I don't know if this helps you in your application. It's really hard
> to say what you should do without knowing more.
>
> Finally, I should point out that if you are working strictly
> interactively, there is the var() function, which performs some magic
> to define symbols for you, like
>
> >>> var('x y z')
> >>> x
>
> x
>
> However, it's not recommended to use this function unless you are
> working interactively, because there can be some subtle issues (e.g.,
> it might not work unless it's called at the module level), and it's
> somewhat bad style.
>
> Another option would be to create the variable definitions
> programitically. The python() function might help. For example:
>
> In [67]: python(symbols("x, y, z, a, b, c, d"))
> Out[67]:
> x = Symbol('x')
> y = Symbol('y')
> z = Symbol('z')
> a = Symbol('a')
> b = Symbol('b')
> c = Symbol('c')
> d = Symbol('d')
> e = (x, y, z, a, b, c, d)
>
> You can take all those definitions and paste them into your file.
>
> Aaron Meurer
>
>
Thank you for the reply.
The following is ugly (and perhaps dangerous), but seems to work:
-----
import sympy as sp
vars = ['mx1','mx2','mx3']
for v in vars:
exec("%s=sp.Symbol('%s')" % (v,v))
print sp.expand((mx1*mx2 + mx3)**2)
-----
Best regards,
Brad
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