Example #1
0
def test_functional_differential_geometry_ch2():
    # From "Functional Differential Geometry" as of 2011
    # by Sussman and Wisdom.
    x0, y0, r0, theta0 = symbols('x0, y0, r0, theta0', real=True)
    x, y, r, theta = symbols('x, y, r, theta', real=True)
    f = Function('f')

    assert (R2_p.point_to_coords(R2_r.point([x0, y0])) ==
                Matrix([sqrt(x0**2+y0**2), atan2(y0, x0)]))
    assert (R2_r.point_to_coords(R2_p.point([r0, theta0])) ==
                Matrix([r0*cos(theta0), r0*sin(theta0)]))
    #TODO jacobian page 12 - 32

    field = ScalarField(R2_r, [x, y], f(x, y))
    p1_in_rect = R2_r.point([x0, y0])
    p1_in_polar = R2_p.point([sqrt(x0**2 + y0**2), atan2(y0,x0)])
    assert field(p1_in_rect) == f(x0, y0)
    # TODO better simplification for the next one
    #print simplify(field(p1_in_polar))
    #assert simplify(field(p1_in_polar)) == f(x0, y0)

    p_r = R2_r.point([x0, y0])
    p_p = R2_p.point([r0, theta0])
    assert R2.x(p_r) == x0
    assert R2.x(p_p) == r0*cos(theta0)
    assert R2.r(p_p) == r0
    assert R2.r(p_r) == sqrt(x0**2 + y0**2)
    assert R2.theta(p_r) == atan2(y0, x0)

    h = R2.x*R2.r**2 + R2.y**3
    assert h(p_r) == x0*(x0**2 + y0**2) + y0**3
    assert h(p_p) == r0**3*sin(theta0)**3 + r0**3*cos(theta0)