Make sympy_to_scipy More efficient

[tBuLi]

def sympy_to_scipy(func, vars, params):
    """
    Convert a symbolic expression to one scipy digs.
    :param func: sympy expression
    :param vars: variables
    :param params: parameters
    """
    lambda_func = sympy_to_py(func, vars, params)
    def f(x, p):
        """
        Scipy style function.
        :param x: list of arrays, NxM
        :param p: tuple of parameter values.
        """
        x = np.atleast_2d(x)
        y = [x[i] for i in range(len(x))]
        return lambda_func(*(y + list(p)))

    return f

The current definition of f will do the list comprehension every time it is called, which can be a lot of a lot of iterations are needed for the fit to converge. Therefore a more efficient function is desirable.

[tBuLi]

No longer relevant due to the internal API changes