I think this would be a great contribution to the SymPy physics module. Can you put some usage doc strings? Then, we can put it in the appropriate places.
-- Andy On Wed, Nov 10, 2010 at 3:10 AM, Philippe <[email protected]> wrote: > some usage if needed.. > this is my unittest file. > the lagrange and partial_derivative functions are in meca.py > > - - - - - - - - - - - - > > import unittest > from sympy import * > import meca > > class MyTest(unittest.TestCase): > > def test_lagrange_1(self): > t = Symbol('t') > x = Function('x')(t) > y = Function('y')(t) > dT_dqvt, dT_dq = meca.lagrange(diff(x, t)**2+diff(y, t)**2 + 5 > * x, [x, y]) > > dT_dqvt_0 = 2*diff(x, t, t) > dT_dqvt_1 = 2*diff(y, t, t) > > self.assertEquals(dT_dqvt, [dT_dqvt_0, dT_dqvt_1]) > self.assertEquals(dT_dq, [5, 0]) > > def test_lagrange_2(self): > t = Symbol('t') > k = Symbol('k') > x = Function('x')(t) > dT_dqvt, dT_dq = meca.lagrange(k*diff(x, t)**2 + k * x, [x]) > > dT_dqvt_0 = 2*k*diff(x, t, t) > > self.assertEquals(dT_dqvt, [dT_dqvt_0]) > self.assertEquals(dT_dq, [k]) > > def test_partial_derivative_1(self): > t = Symbol('t') > k = Symbol('k') > x = Function('x')(t) > dE_q = meca.partial_derivative(k*diff(x, t)**2 + k * x, x) > dE_q_sol = k > self.assertEquals(dE_q, dE_q_sol) > > def test_partial_derivative_2(self): > t = Symbol('t') > k = Symbol('k') > x = Function('x')(t) > dE_q = meca.partial_derivative(k*diff(x, t)**2 + k * x, > diff(x, t)) > dE_q_sol = 2*k*diff(x, t) > self.assertEquals(dE_q, dE_q_sol) > > > if __name__ == '__main__': > unittest.main() > > - - - - - - - - - - - - > > On 9 nov, 17:18, Philippe <[email protected]> wrote: >> from sympy import * >> >> t = Symbol('t') >> x = Function('x')(t) >> y = Function('y')(t) >> >> def partial_derivative(equa, param): >> param_sub = Symbol('param_sub') >> equa_subs1 = equa.subs(param, param_sub) >> dequa_param_sub = diff(equa_subs1, param_sub) >> dequa_param = dequa_param_sub.subs(param_sub, param) >> return dequa_param >> >> def lagrange(equa, param): >> """ >> param is a list of Function of time >> must not use 'q1', 'q2', .... 'qv1', ... in the equation >> """ >> vel_var = [diff(e, t) for e in param] >> dT_dqv = [partial_derivative(equa, p) for p in vel_var] >> dT_dq = [partial_derivative(equa, p) for p in param] >> >> dT_dqvt = [diff(e, t) for e in dT_dqv] >> >> return dT_dqvt, dT_dq >> >> On 31 oct, 20:51, Tim Lahey <[email protected]> wrote: >> >> > On Sun, Oct 31, 2010 at 3:41 PM, Aaron S. Meurer <[email protected]> >> > wrote: >> >> > > I am still trying to fully understand the code below, but if one of the >> > > subs is trying to do something like diff(f(x), x).subs(x, g(x)), then >> > > you will get an error in SymPy for the above reason. >> >> > > Aaron Meurer >> >> > The basic approach is to substitute a symbol for f(x) say f1 and then >> > take the derivative >> > with respect to that. You know the substitution, so you can reverse >> > it. Once the derivative >> > is done, you reverse the substitution. Then, you can take the >> > derivative with respect to >> > x. >> >> > So, the steps become. >> >> > 1. Build list of symbols for functions. >> > 2. Build a list of substitutions for the functions and the reverse. >> > 3. Substitute for the functions. >> > 4. Run derivatives with respect to the symbols. >> > 5. Substitute functions for the symbols. >> > 6. Take any derivatives with respect to the function variables. >> >> > Hope that helps the explanation. A lot of what's done in the code is using >> > zip and map to make the code fast, but I originally wrote it as above. >> > Python >> > has appropriate functions that this should still be fast. >> >> > Cheers, >> >> > Tim. >> >> > -- >> > Tim Lahey >> > PhD Candidate, Systems Design Engineering >> > University of Waterloohttp://www.linkedin.com/in/timlahey >> >> > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
