Adding Symbol('t') to the free_symbols property of my class worked!
Here's what it can do now:
In [1]: run kinematics.py
In [2]: x = TVS('x')
In [3]: y = TVS('y')
In [4]: t = Symbol('t')
In [5]: diff(2 * x**2 + 4 + y,t)
Out[5]: 4*x*xdt + ydt
In [7]: diff(diff(2 * x**2 + 4 + y,t),TVS('xdt'))
Out[7]: 4*x
TVS is timevaryingsymbol, athough I think Renato's DynamicSymbol
sounds better.
I think this is exactly what I wanted; Thanks!
-Gilbert
On Jun 4, 7:16 am, Chris Smith <[email protected]> wrote:
> It would help me understand if you gave an example input/output pair so I
> could see what you were wanting to do. I did look at the gist but didn't see
> the output that you wanted. Would idiff be of any use?
>
> >>> help(idiff)
> Help on function idiff in module sympy.geometry.util:
>
> idiff(eq, y, x, dep=None)
> Return dy/dx assuming that y and any other variables given in dep
> depend on x.
>
> >>> from sympy.abc import x, y, a
> >>> from sympy.geometry.util import idiff
>
> >>> idiff(x**2 + y**2 - 4, y, x)
> -x/y
> >>> idiff(x + a + y, y, x)
> -1
> >>> idiff(x + a + y, y, x, [a])
> -D(a, x) - 1
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