On Monday, May 25, 2015 at 12:07:22 AM UTC-5, dori...@berkeley.edu wrote:
>
> Hi all,
>
> I am new to SymPy and I am trying to rearrange equations in order to
> express one variable in terms of another in SymPy.
> For example, I have two physics equations F=ma and rho=m/v which I defined
> in the beginning. I want to re-express ``a`` in terms of f,rho, and v.
> However, the ``solve`` function sets the right hand side of the equation
> so that it is equal to zero so then when I try to get ``a`` in terms of `f`
> it returns zero.
> Is there a way I could do this SymPy, if so, which function should I be
> looking at instead?
>
>
>
Instead of defining a Python symbol, e.g. f = m*a, define an equation
containing the symbols of interest, e.g. e1 = Eq(f, ma). Then, when
solving, tell solve what you *don't* want to solve for and it will attempt
to solve for the remaining symbols:
>>> e1=Eq(f,m*a)
>>> e2=Eq(rho,m*v)
>>> solve((e1,e2),exclude=[f,rho,v]) # i.e. solve for m and a
[{m: rho/v, a: f*v/rho}]
>>>
/c
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