How to import symbolic expressions from Python to MATLAB?

One of my colleagues is using Python(more specifically SymPy) to generate a very big symbolic expression. Now, I want to perform some numerical computations on the expression in MATLAB. How can I export the expression from Python and import it in MATLAB?

Answer 1

[Michael Croucher]

Imagine your friend had a Python function that created that expression. Let's call it create_symbolic_expression() and put it into a file sympy_demo.py. My demonstration is likely to be more simple than the one you have in mind.

sympy_demo.py also contains a function that lambdify's this symbolic expression..that is, it creates a Python function in the variables x,y and z.

%This is the contents of sympy_demo.py
from sympy import lambdify
from sympy.abc import x,y,z

def create_symbolic_expression():
    '''
    This is a proxy for whatever code your friend has written but I'll keep it simple for this demo.
    '''
    expr = x+y+z
    return(x+y+z)

def lambdify_expression(expr):
    return(lambdify([x,y,z],expr))

We can now go to MATLAB, ensure sympy_demo.py is on your path and do

import py.sympy_demo.create_symbolic_expression
import py.sympy_demo.lambdify_expression
expr = create_symbolic_expression()   %This is a Python object in MATLAB that represents the symbolic expression
myfunc = lambdify_expression(expr)   %Turn it into a Python function that can be evaluated in MATLAB

We can now evaluate myfunc with numeric inputs

myfunc(1,2,3)
ans =
     6

[Sayan Batabyal]

Thanks for your answer. It worked.

[Benedikt]

The % character in sympy_demo.py produces an error. Use # for python comment.