def rotx(t):
    """Rotation about the x-axis."""
    c = np.cos(t)
    s = np.sin(t)
    return np.array([[1,  0,  0],
                     [0,  c, -s],
                     [0,  s,  c]])
def rotx ( t ) : c = np . cos ( t ) s = np . sin ( t ) return np . array ( [ [ 1 , 0 , 0 ] , [ 0 , c , - s ] , [ 0 , s , c ] ] )
Rotation about the x-axis.