queries.py 文件源码

def q_affine(expr, vars):
    """
    Return True if ``expr`` is (separately) affine in the variables ``vars``,
    False otherwise.

    Readapted from: https://stackoverflow.com/questions/36283548\
        /check-if-an-equation-is-linear-for-a-specific-set-of-variables/
    """
    # A function is (separately) affine in a given set of variables if all
    # non-mixed second order derivatives are identically zero.
    for x in as_tuple(vars):
        if x not in expr.atoms():
            return False
        try:
            if diff(expr, x) == nan or not Eq(diff(expr, x, x), 0):
                return False
        except TypeError:
            return False
    return True