On 20/01/2014 22:09, rpi.bal...@gmail.com wrote:
Hey all,
I'm new at Python, so if you see any mistakes feel free to let me know.
I'm trying to take a symbolic expression and turn it into a variable equation
or function. I think that just an expression of variables would be preferable.
I have a range equation which I form using symbols and then take various
derivatives of it. I then want to have these derivatives on hand to use for
various functions, but short of using sub every time or just copy pasting from
the console output (I don't want to do that), I can't find an efficient way to
do this. Matlab had matlabFunction which was really handy, but I don't think
Python has an equivalent.
########
import numpy as np
import scipy as sp
import sympy as sy
import math as ma
x, y, z, x_s, y_s, z_s, theta, theta_dot, x_dot, y_dot, z_dot = sy.symbols('x y
z x_s y_s z_s theta theta_dot x_dot y_dot z_dot')
rho = (x**2 + y**2 + z**2 + x_s**2 + y_s**2 + z_s**2 - 2*(x*x_s +
y*y_s)*sy.cos(theta) + 2*(x*y_s - y*x_s)*sy.sin(theta) - 2*z*z_s)**(0.5)
rho_dot = (x*x_dot + y*y_dot + z*z_dot - (x_dot*x_s + y_dot*y_s)*sy.cos(theta)
+ theta_dot*(x*x_s + y*y_s)*sy.sin(theta) + (x_dot*y_s -
y_dot*x_s)*sy.sin(theta) + theta_dot*(x*y_s - y*x_s)*sy.cos(theta) -
z_dot*z_s)/rho
drho_dx = sy.diff(rho, x)
drho_dy = sy.diff(rho, y)
drho_dz = sy.diff(rho, z)
#I then want drho_dx, etc to be variable expressions with x, y, z, etc as
variables instead of symbols or numbers. I could do:
x, y, z = 1200, 1300, 1400 #m
drho_dx = subs([x, x], [y, y], [z, z])
#but this seems inefficient to do multiple times. Thoughts?
There are references to MatlabFunction in code here
https://github.com/scipy/scipy/tree/master/scipy/io/matlab but I haven't
the faintest idea as to whether or not it does what you want, sorry :(
--
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.
Mark Lawrence
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