import math


def angle_dev(a, b):
    """
    Computes the minimum signed difference between two radian angles.

    Parameters
    ----------
    a: float
        angle A
    b: float
        angle B

    Returns
    -------
    float
        difference between A and B
    """
    diff = math.fmod((a - b + math.pi), (math.pi * 2)) - math.pi
    return diff