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

    Returns a dictionary of the gradients.

def logp_gradient_of_set(variable_set, calculation_set=None):
    """
    Calculates the gradient of the joint log posterior with respect to all the variables in variable_set.
    Calculation of the log posterior is restricted to the variables in calculation_set.

    Returns a dictionary of the gradients.
    """

    logp_gradients = {}
    for variable in variable_set:
        logp_gradients[variable] = logp_gradient(variable, calculation_set)

    return logp_gradients