Calculates the gradient of the joint log posterior with respect to variable.
    Calculation of the log posterior is restricted to the variables in calculation_set.

def logp_gradient(variable, calculation_set=None):
    """
    Calculates the gradient of the joint log posterior with respect to variable.
    Calculation of the log posterior is restricted to the variables in calculation_set.
    """
    return variable.logp_partial_gradient(variable, calculation_set) + sum(
        [child.logp_partial_gradient(variable, calculation_set) for child in variable.children])