def test_Series_str():
tf1 = TransferFunction(x * y**2 - z, y**3 - t**3, y)
tf2 = TransferFunction(x - y, x + y, y)
tf3 = TransferFunction(t * x**2 - t**w * x + w, t - y, y)
assert str(Series(tf1, tf2)) == \
"Series(TransferFunction(x*y**2 - z, -t**3 + y**3, y), TransferFunction(x - y, x + y, y))"
assert str(Series(tf1, tf2, tf3)) == \
"Series(TransferFunction(x*y**2 - z, -t**3 + y**3, y), TransferFunction(x - y, x + y, y), TransferFunction(t*x**2 - t**w*x + w, t - y, y))"
assert str(Series(-tf2, tf1)) == \
"Series(TransferFunction(-x + y, x + y, y), TransferFunction(x*y**2 - z, -t**3 + y**3, y))"
def test_Feedback_construction():
zeta, wn = symbols('zeta, wn')
tf1 = TransferFunction(1, s**2 + 2 * zeta * wn * s + wn**2, s)
tf2 = TransferFunction(k, 1, s)
tf3 = TransferFunction(a2 * p - s, a2 * s + p, s)
tf4 = TransferFunction(a0 * p + p**a1 - s, p, p)
tf5 = TransferFunction(a1 * s**2 + a2 * s - a0, s + a0, s)
tf6 = TransferFunction(s - p, p + s, p)
f1 = Feedback(TransferFunction(1, 1, s), tf1 * tf2 * tf3)
assert f1.args == (TransferFunction(1, 1, s), Series(tf1, tf2, tf3))
assert f1.num == TransferFunction(1, 1, s)
assert f1.den == Series(tf1, tf2, tf3)
assert f1.var == s
f2 = Feedback(tf1, tf2 * tf3)
assert f2.args == (tf1, Series(tf2, tf3))
assert f2.num == tf1
assert f2.den == Series(tf2, tf3)
assert f2.var == s
f3 = Feedback(tf1 * tf2, tf5)
assert f3.args == (Series(tf1, tf2), tf5)
assert f3.num == Series(tf1, tf2)
f4 = Feedback(tf4, tf6)
assert f4.args == (tf4, tf6)
assert f4.num == tf4
assert f4.var == p
f5 = Feedback(tf5, TransferFunction(1, 1, s))
assert f5.args == (tf5, TransferFunction(1, 1, s))
assert f5.var == s
f6 = Feedback(TransferFunction(1, 1, p), tf4)
assert f6.args == (TransferFunction(1, 1, p), tf4)
assert f6.var == p
f7 = -Feedback(tf4 * tf6, TransferFunction(1, 1, p))
assert f7.args == (Series(TransferFunction(-1, 1, p),
Series(tf4, tf6)), TransferFunction(1, 1, p))
assert f7.num == Series(TransferFunction(-1, 1, p), Series(tf4, tf6))
# denominator can't be a Parallel instance
raises(TypeError, lambda: Feedback(tf1, tf2 + tf3))
raises(TypeError, lambda: Feedback(tf1, Matrix([1, 2, 3])))
raises(TypeError, lambda: Feedback(TransferFunction(1, 1, s), s - 1))
raises(TypeError, lambda: Feedback(1, 1))
raises(
ValueError,
lambda: Feedback(TransferFunction(1, 1, s), TransferFunction(1, 1, s)))
raises(ValueError, lambda: Feedback(tf2, tf4 * tf5))
def test_Parallel_construction():
zeta, wn = symbols('zeta, wn')
tf = TransferFunction(a0 * s**3 + a1 * s**2 - a2 * s,
b0 * p**4 + b1 * p**3 - b2 * s * p, s)
tf2 = TransferFunction(a2 * p - s, a2 * s + p, s)
tf3 = TransferFunction(a0 * p + p**a1 - s, p, p)
tf4 = TransferFunction(1, s**2 + 2 * zeta * wn * s + wn**2, s)
inp = Function('X_d')(s)
out = Function('X')(s)
p0 = Parallel(tf, tf2)
assert p0.args == (tf, tf2)
assert p0.var == s
p1 = Parallel(Series(tf, -tf2), tf2)
assert p1.args == (Series(tf, -tf2), tf2)
assert p1.var == s
tf3_ = TransferFunction(inp, 1, s)
tf4_ = TransferFunction(-out, 1, s)
p2 = Parallel(tf, Series(tf3_, -tf4_), tf2)
assert p2.args == (tf, Series(tf3_, -tf4_), tf2)
p3 = Parallel(tf, tf2, tf4)
assert p3.args == (tf, tf2, tf4)
p4 = Parallel(tf3_, tf4_)
assert p4.args == (tf3_, tf4_)
assert p4.var == s
p5 = Parallel(tf, tf2)
assert p0 == p5
assert not p0 == p1
p6 = Parallel(tf2, tf4, Series(tf2, -tf4))
assert p6.args == (tf2, tf4, Series(tf2, -tf4))
p7 = Parallel(tf2, tf4, Series(tf2, -tf), tf4)
assert p7.args == (tf2, tf4, Series(tf2, -tf), tf4)
raises(ValueError, lambda: Parallel(tf, tf3))
raises(ValueError, lambda: Parallel(tf, tf2, tf3, tf4))
raises(ValueError, lambda: Parallel(-tf3, tf4))
raises(TypeError, lambda: Parallel(2, tf, tf4))
raises(TypeError, lambda: Parallel(s**2 + p * s, tf3, tf2))
raises(TypeError, lambda: Parallel(tf3, Matrix([1, 2, 3, 4])))
def test_TransferFunction_multiplication_and_division():
G1 = TransferFunction(s + 3, -s**3 + 9, s)
G2 = TransferFunction(s + 1, s - 5, s)
G3 = TransferFunction(p, p**4 - 6, p)
G4 = TransferFunction(p + 4, p - 5, p)
G5 = TransferFunction(s + 6, s - 5, s)
G6 = TransferFunction(s + 3, s + 1, s)
G7 = TransferFunction(1, 1, s)
# multiplication
assert G1*G2 == Series(G1, G2)
assert -G1*G5 == Series(-G1, G5)
assert -G2*G5*-G6 == Series(-G2, G5, -G6)
assert -G1*-G2*-G5*-G6 == Series(-G1, -G2, -G5, -G6)
assert G3*G4 == Series(G3, G4)
assert (G1*G2)*-(G5*G6) == \
Series(G1, G2, TransferFunction(-1, 1, s), Series(G5, G6))
assert G1*G2*(G5 + G6) == Series(G1, G2, Parallel(G5, G6))
c = symbols("c", commutative=False)
raises(ValueError, lambda: G3 * Matrix([1, 2, 3]))
raises(ValueError, lambda: G1 * c)
raises(ValueError, lambda: G3 * G5)
raises(ValueError, lambda: G5 * (s - 1))
raises(ValueError, lambda: 9 * G5)
raises(ValueError, lambda: G3 / Matrix([1, 2, 3]))
raises(ValueError, lambda: G6 / 0)
raises(ValueError, lambda: G3 / G5)
raises(ValueError, lambda: G5 / 2)
raises(ValueError, lambda: G5 / s**2)
raises(ValueError, lambda: (s - 4*s**2) / G2)
raises(ValueError, lambda: 0 / G4)
raises(ValueError, lambda: G5 / G6)
raises(ValueError, lambda: -G3 /G4)
raises(ValueError, lambda: G7 / (1 + G6))
raises(ValueError, lambda: G7 / (G5 * G6))
raises(ValueError, lambda: G7 / (G7 + (G5 + G6)))
import_kwargs={'fromlist': ['pyplot']},
catch=(RuntimeError, ))
numpy = import_module('numpy')
tf1 = TransferFunction(1, p**2 + 0.5 * p + 2, p)
tf2 = TransferFunction(p, 6 * p**2 + 3 * p + 1, p)
tf3 = TransferFunction(p, p**3 - 1, p)
tf4 = TransferFunction(10, p**3, p)
tf5 = TransferFunction(5, s**2 + 2 * s + 10, s)
tf6 = TransferFunction(1, 1, s)
tf7 = TransferFunction(4 * s * 3 + 9 * s**2 + 0.1 * s + 11,
8 * s**6 + 9 * s**4 + 11, s)
tf8 = TransferFunction(5, s**2 + (2 + I) * s + 10, s)
ser1 = Series(tf4, TransferFunction(1, p - 5, p))
ser2 = Series(tf3, TransferFunction(p, p + 2, p))
par1 = Parallel(tf1, tf2)
par2 = Parallel(tf1, tf2, tf3)
def _to_tuple(a, b):
return tuple(a), tuple(b)
def _trim_tuple(a, b):
a, b = _to_tuple(a, b)
return tuple(a[0: 2] + a[len(a)//2 : len(a)//2 + 1] + a[-2:]), \
tuple(b[0: 2] + b[len(b)//2 : len(b)//2 + 1] + b[-2:])
def test_Parallel_functions():
zeta, wn = symbols('zeta, wn')
tf1 = TransferFunction(1, s**2 + 2*zeta*wn*s + wn**2, s)
tf2 = TransferFunction(k, 1, s)
tf3 = TransferFunction(a2*p - s, a2*s + p, s)
tf4 = TransferFunction(a0*p + p**a1 - s, p, p)
tf5 = TransferFunction(a1*s**2 + a2*s - a0, s + a0, s)
assert tf1 + tf2 + tf3 == Parallel(tf1, tf2, tf3)
assert tf1 + tf2 + tf3 + tf5 == Parallel(tf1, tf2, tf3, tf5)
assert tf1 + tf2 - tf3 - tf5 == Parallel(tf1, tf2, -tf3, -tf5)
assert tf1 + tf2*tf3 == Parallel(tf1, Series(tf2, tf3))
assert tf1 - tf2*tf3 == Parallel(tf1, -Series(tf2,tf3))
assert -tf1 - tf2 == Parallel(-tf1, -tf2)
assert -(tf1 + tf2) == Series(TransferFunction(-1, 1, s), Parallel(tf1, tf2))
assert (tf2 + tf3)*tf1 == Series(Parallel(tf2, tf3), tf1)
assert (tf1 + tf2)*(tf3*tf5) == Series(Parallel(tf1, tf2), tf3, tf5)
assert -(tf2 + tf3)*-tf5 == Series(TransferFunction(-1, 1, s), Parallel(tf2, tf3), -tf5)
assert tf2 + tf3 + tf2*tf1 + tf5 == Parallel(tf2, tf3, Series(tf2, tf1), tf5)
assert tf2 + tf3 + tf2*tf1 - tf3 == Parallel(tf2, tf3, Series(tf2, tf1), -tf3)
assert (tf1 + tf2 + tf5)*(tf3 + tf5) == Series(Parallel(tf1, tf2, tf5), Parallel(tf3, tf5))
raises(ValueError, lambda: tf1 + tf2 + tf4)
raises(ValueError, lambda: tf1 - tf2*tf4)
raises(ValueError, lambda: tf3 + Matrix([1, 2, 3]))
# evaluate=True -> doit()
assert Parallel(tf1, tf2, evaluate=True) == Parallel(tf1, tf2).doit() == \
TransferFunction(k*(s**2 + 2*s*wn*zeta + wn**2) + 1, s**2 + 2*s*wn*zeta + wn**2, s)
assert Parallel(tf1, tf2, Series(-tf1, tf3), evaluate=True) == \
Parallel(tf1, tf2, Series(-tf1, tf3)).doit()== TransferFunction((-a2*p + s)*(s**2 + 2*s*wn*zeta + wn**2) + \
(a2*s + p)*(k*(s**2 + 2*s*wn*zeta + wn**2) + 1)*(s**2 + 2*s*wn*zeta + wn**2), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2)**2, s)
assert Parallel(tf2, tf1, -tf3, evaluate=True) == Parallel(tf2, tf1, -tf3).doit() == \
TransferFunction(-(a2*p - s)*(s**2 + 2*s*wn*zeta + wn**2) + (a2*s + p)*(k*(s**2 + 2*s*wn*zeta + wn**2) + 1), \
(a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert not Parallel(tf1, -tf2, evaluate=False) == Parallel(tf1, -tf2).doit()
assert Parallel(Series(tf1, tf2), Series(tf2, tf3)).doit() == \
TransferFunction(k*(a2*p - s)*(s**2 + 2*s*wn*zeta + wn**2) + k*(a2*s + p), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Parallel(-tf1, -tf2, -tf3).doit() == \
TransferFunction(-(a2*p - s)*(s**2 + 2*s*wn*zeta + wn**2) + \
(a2*s + p)*(-k*(s**2 + 2*s*wn*zeta + wn**2) - 1), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert -Parallel(tf1, tf2, tf3).doit() == \
TransferFunction(-((a2*p - s)*(s**2 + 2*s*wn*zeta + wn**2) + (a2*s + p)*(k*(s**2 + 2*s*wn*zeta + wn**2) + 1)),
(a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Parallel(tf2, tf3, Series(tf2, -tf1), tf3).doit() == \
TransferFunction((a2*p - s)*(a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2) + (a2*s + p)*(-k*(a2*s + p) + \
(s**2 + 2*s*wn*zeta + wn**2)*(a2*p + k*(a2*s + p) - s)), (a2*s + p)**2*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Parallel(tf1, tf2).rewrite(TransferFunction) == \
TransferFunction(k*(s**2 + 2*s*wn*zeta + wn**2) + 1, s**2 + 2*s*wn*zeta + wn**2, s)
assert Parallel(tf2, tf1, -tf3).rewrite(TransferFunction) == \
TransferFunction(-(a2*p - s)*(s**2 + 2*s*wn*zeta + wn**2) + (a2*s + p)*(k*(s**2 + 2*s*wn*zeta + wn**2) + 1), \
(a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
P1 = Parallel(Series(tf1, tf2), Series(tf2, tf3))
assert P1.is_proper
assert not P1.is_strictly_proper
assert P1.is_biproper
P2 = Parallel(tf1, -tf2, -tf3)
assert P2.is_proper
assert not P2.is_strictly_proper
assert P2.is_biproper
P3 = Parallel(tf1, -tf2, Series(tf1, tf3))
assert P3.is_proper
assert not P3.is_strictly_proper
assert P3.is_biproper
def test_Series_functions():
zeta, wn = symbols('zeta, wn')
tf1 = TransferFunction(1, s**2 + 2*zeta*wn*s + wn**2, s)
tf2 = TransferFunction(k, 1, s)
tf3 = TransferFunction(a2*p - s, a2*s + p, s)
tf4 = TransferFunction(a0*p + p**a1 - s, p, p)
tf5 = TransferFunction(a1*s**2 + a2*s - a0, s + a0, s)
assert tf1*tf2*tf3 == Series(tf1, tf2, tf3)
assert tf1*(tf2 + tf3) == Series(tf1, Parallel(tf2, tf3))
assert tf1*tf2 + tf5 == Parallel(Series(tf1, tf2), tf5)
assert tf1*tf2 - tf5 == Parallel(Series(tf1, tf2), -tf5)
assert tf1*tf2 + tf3 + tf5 == Parallel(Series(tf1, tf2), tf3, tf5)
assert tf1*tf2 - tf3 - tf5 == Parallel(Series(tf1, tf2), -tf3, -tf5)
assert tf1*tf2 - tf3 + tf5 == Parallel(Series(tf1, tf2), -tf3, tf5)
assert tf1*tf2 + tf3*tf5 == Parallel(Series(tf1, tf2), Series(tf3, tf5))
assert tf1*tf2 - tf3*tf5 == Parallel(Series(tf1, tf2), Series(TransferFunction(-1, 1, s), Series(tf3, tf5)))
assert tf2*tf3*(tf2 - tf1)*tf3 == Series(tf2, tf3, Parallel(tf2, -tf1), tf3)
assert -tf1*tf2 == Series(-tf1, tf2)
assert -(tf1*tf2) == Series(TransferFunction(-1, 1, s), Series(tf1, tf2))
raises(ValueError, lambda: tf1*tf2*tf4)
raises(ValueError, lambda: tf1*(tf2 - tf4))
raises(ValueError, lambda: tf3*Matrix([1, 2, 3]))
# evaluate=True -> doit()
assert Series(tf1, tf2, evaluate=True) == Series(tf1, tf2).doit() == \
TransferFunction(k, s**2 + 2*s*wn*zeta + wn**2, s)
assert Series(tf1, tf2, Parallel(tf1, -tf3), evaluate=True) == Series(tf1, tf2, Parallel(tf1, -tf3)).doit() == \
TransferFunction(k*(a2*s + p + (-a2*p + s)*(s**2 + 2*s*wn*zeta + wn**2)), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2)**2, s)
assert Series(tf2, tf1, -tf3, evaluate=True) == Series(tf2, tf1, -tf3).doit() == \
TransferFunction(k*(-a2*p + s), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert not Series(tf1, -tf2, evaluate=False) == Series(tf1, -tf2).doit()
assert Series(Parallel(tf1, tf2), Parallel(tf2, -tf3)).doit() == \
TransferFunction((k*(s**2 + 2*s*wn*zeta + wn**2) + 1)*(-a2*p + k*(a2*s + p) + s), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Series(-tf1, -tf2, -tf3).doit() == \
TransferFunction(k*(-a2*p + s), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert -Series(tf1, tf2, tf3).doit() == \
TransferFunction(-k*(a2*p - s), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Series(tf2, tf3, Parallel(tf2, -tf1), tf3).doit() == \
TransferFunction(k*(a2*p - s)**2*(k*(s**2 + 2*s*wn*zeta + wn**2) - 1), (a2*s + p)**2*(s**2 + 2*s*wn*zeta + wn**2), s)
assert Series(tf1, tf2).rewrite(TransferFunction) == TransferFunction(k, s**2 + 2*s*wn*zeta + wn**2, s)
assert Series(tf2, tf1, -tf3).rewrite(TransferFunction) == \
TransferFunction(k*(-a2*p + s), (a2*s + p)*(s**2 + 2*s*wn*zeta + wn**2), s)
S1 = Series(Parallel(tf1, tf2), Parallel(tf2, -tf3))
assert S1.is_proper
assert not S1.is_strictly_proper
assert S1.is_biproper
S2 = Series(tf1, tf2, tf3)
assert S2.is_proper
assert S2.is_strictly_proper
assert not S2.is_biproper
S3 = Series(tf1, -tf2, Parallel(tf1, -tf3))
assert S3.is_proper
assert S3.is_strictly_proper
assert not S3.is_biproper
def test_Series_construction():
zeta, wn = symbols('zeta, wn')
tf = TransferFunction(a0*s**3 + a1*s**2 - a2*s, b0*p**4 + b1*p**3 - b2*s*p, s)
tf2 = TransferFunction(a2*p - s, a2*s + p, s)
tf3 = TransferFunction(a0*p + p**a1 - s, p, p)
tf4 = TransferFunction(1, s**2 + 2*zeta*wn*s + wn**2, s)
inp = Function('X_d')(s)
out = Function('X')(s)
s0 = Series(tf, tf2)
assert s0.args == (tf, tf2)
assert s0.var == s
s1 = Series(Parallel(tf, -tf2), tf2)
assert s1.args == (Parallel(tf, -tf2), tf2)
assert s1.var == s
tf3_ = TransferFunction(inp, 1, s)
tf4_ = TransferFunction(-out, 1, s)
s2 = Series(tf, Parallel(tf3_, tf4_), tf2)
assert s2.args == (tf, Parallel(tf3_, tf4_), tf2)
s3 = Series(tf, tf2, tf4)
assert s3.args == (tf, tf2, tf4)
s4 = Series(tf3_, tf4_)
assert s4.args == (tf3_, tf4_)
assert s4.var == s
s6 = Series(tf2, tf4, Parallel(tf2, -tf), tf4)
assert s6.args == (tf2, tf4, Parallel(tf2, -tf), tf4)
s7 = Series(tf, tf2)
assert s0 == s7
assert not s0 == s2
raises(ValueError, lambda: Series(tf, tf3))
raises(ValueError, lambda: Series(tf, tf2, tf3, tf4))
raises(ValueError, lambda: Series(-tf3, tf2))
raises(TypeError, lambda: Series(2, tf, tf4))
raises(TypeError, lambda: Series(s**2 + p*s, tf3, tf2))
raises(TypeError, lambda: Series(tf3, Matrix([1, 2, 3, 4])))
def test_TransferFunction_functions():
# explicitly cancel poles and zeros.
tf0 = TransferFunction(s**5 + s**3 + s, s - s**2, s)
a = TransferFunction(-(s**4 + s**2 + 1), s - 1, s)
assert tf0.simplify() == simplify(tf0) == a
tf1 = TransferFunction((p + 3)*(p - 1), (p - 1)*(p + 5), p)
b = TransferFunction(p + 3, p + 5, p)
assert tf1.simplify() == simplify(tf1) == b
# expand the numerator and the denominator.
G1 = TransferFunction((1 - s)**2, (s**2 + 1)**2, s)
G2 = TransferFunction(1, -3, p)
c = (a2*s**p + a1*s**s + a0*p**p)*(p**s + s**p)
d = (b0*s**s + b1*p**s)*(b2*s*p + p**p)
e = a0*p**p*p**s + a0*p**p*s**p + a1*p**s*s**s + a1*s**p*s**s + a2*p**s*s**p + a2*s**(2*p)
f = b0*b2*p*s*s**s + b0*p**p*s**s + b1*b2*p*p**s*s + b1*p**p*p**s
g = a1*a2*s*s**p + a1*p*s + a2*b1*p*s*s**p + b1*p**2*s
G3 = TransferFunction(c, d, s)
G4 = TransferFunction(a0*s**s - b0*p**p, (a1*s + b1*s*p)*(a2*s**p + p), p)
assert G1.expand() == TransferFunction(s**2 - 2*s + 1, s**4 + 2*s**2 + 1, s)
assert tf1.expand() == TransferFunction(p**2 + 2*p - 3, p**2 + 4*p - 5, p)
assert G2.expand() == G2
assert G3.expand() == TransferFunction(e, f, s)
assert G4.expand() == TransferFunction(a0*s**s - b0*p**p, g, p)
# purely symbolic polynomials.
p1 = a1*s + a0
p2 = b2*s**2 + b1*s + b0
SP1 = TransferFunction(p1, p2, s)
expect1 = TransferFunction(2.0*s + 1.0, 5.0*s**2 + 4.0*s + 3.0, s)
expect1_ = TransferFunction(2*s + 1, 5*s**2 + 4*s + 3, s)
assert SP1.subs({a0: 1, a1: 2, b0: 3, b1: 4, b2: 5}) == expect1_
assert SP1.subs({a0: 1, a1: 2, b0: 3, b1: 4, b2: 5}).evalf() == expect1
assert expect1_.evalf() == expect1
c1, d0, d1, d2 = symbols('c1, d0:3')
p3, p4 = c1*p, d2*p**3 + d1*p**2 - d0
SP2 = TransferFunction(p3, p4, p)
expect2 = TransferFunction(2.0*p, 5.0*p**3 + 2.0*p**2 - 3.0, p)
expect2_ = TransferFunction(2*p, 5*p**3 + 2*p**2 - 3, p)
assert SP2.subs({c1: 2, d0: 3, d1: 2, d2: 5}) == expect2_
assert SP2.subs({c1: 2, d0: 3, d1: 2, d2: 5}).evalf() == expect2
assert expect2_.evalf() == expect2
SP3 = TransferFunction(a0*p**3 + a1*s**2 - b0*s + b1, a1*s + p, s)
expect3 = TransferFunction(2.0*p**3 + 4.0*s**2 - s + 5.0, p + 4.0*s, s)
expect3_ = TransferFunction(2*p**3 + 4*s**2 - s + 5, p + 4*s, s)
assert SP3.subs({a0: 2, a1: 4, b0: 1, b1: 5}) == expect3_
assert SP3.subs({a0: 2, a1: 4, b0: 1, b1: 5}).evalf() == expect3
assert expect3_.evalf() == expect3
SP4 = TransferFunction(s - a1*p**3, a0*s + p, p)
expect4 = TransferFunction(7.0*p**3 + s, p - s, p)
expect4_ = TransferFunction(7*p**3 + s, p - s, p)
assert SP4.subs({a0: -1, a1: -7}) == expect4_
assert SP4.subs({a0: -1, a1: -7}).evalf() == expect4
assert expect4_.evalf() == expect4
# Low-frequency (or DC) gain.
assert tf0.dc_gain() == 1
assert tf1.dc_gain() == Rational(3, 5)
assert SP2.dc_gain() == 0
assert expect4.dc_gain() == -1
assert expect2_.dc_gain() == 0
assert TransferFunction(1, s, s).dc_gain() == oo
# Poles of a transfer function.
tf_ = TransferFunction(x**3 - k, k, x)
_tf = TransferFunction(k, x**4 - k, x)
TF_ = TransferFunction(x**2, x**10 + x + x**2, x)
_TF = TransferFunction(x**10 + x + x**2, x**2, x)
assert G1.poles() == [I, I, -I, -I]
assert G2.poles() == []
assert tf1.poles() == [-5, 1]
assert expect4_.poles() == [s]
assert SP4.poles() == [-a0*s]
assert expect3.poles() == [-0.25*p]
assert str(expect2.poles()) == str([0.729001428685125, -0.564500714342563 - 0.710198984796332*I, -0.564500714342563 + 0.710198984796332*I])
assert str(expect1.poles()) == str([-0.4 - 0.66332495807108*I, -0.4 + 0.66332495807108*I])
assert _tf.poles() == [k**(Rational(1, 4)), -k**(Rational(1, 4)), I*k**(Rational(1, 4)), -I*k**(Rational(1, 4))]
assert TF_.poles() == [CRootOf(x**9 + x + 1, 0), 0, CRootOf(x**9 + x + 1, 1), CRootOf(x**9 + x + 1, 2),
CRootOf(x**9 + x + 1, 3), CRootOf(x**9 + x + 1, 4), CRootOf(x**9 + x + 1, 5), CRootOf(x**9 + x + 1, 6),
CRootOf(x**9 + x + 1, 7), CRootOf(x**9 + x + 1, 8)]
raises(NotImplementedError, lambda: TransferFunction(x**2, a0*x**10 + x + x**2, x).poles())
# Stability of a transfer function.
q, r = symbols('q, r', negative=True)
t = symbols('t', positive=True)
TF_ = TransferFunction(s**2 + a0 - a1*p, q*s - r, s)
stable_tf = TransferFunction(s**2 + a0 - a1*p, q*s - 1, s)
stable_tf_ = TransferFunction(s**2 + a0 - a1*p, q*s - t, s)
assert G1.is_stable() is False
assert G2.is_stable() is True
assert tf1.is_stable() is False # as one pole is +ve, and the other is -ve.
assert expect2.is_stable() is False
assert expect1.is_stable() is True
assert stable_tf.is_stable() is True
assert stable_tf_.is_stable() is True
assert TF_.is_stable() is False
assert expect4_.is_stable() is None # no assumption provided for the only pole 's'.
assert SP4.is_stable() is None
# Zeros of a transfer function.
assert G1.zeros() == [1, 1]
assert G2.zeros() == []
assert tf1.zeros() == [-3, 1]
assert expect4_.zeros() == [7**(Rational(2, 3))*(-s)**(Rational(1, 3))/7, -7**(Rational(2, 3))*(-s)**(Rational(1, 3))/14 -
sqrt(3)*7**(Rational(2, 3))*I*(-s)**(Rational(1, 3))/14, -7**(Rational(2, 3))*(-s)**(Rational(1, 3))/14 + sqrt(3)*7**(Rational(2, 3))*I*(-s)**(Rational(1, 3))/14]
assert SP4.zeros() == [(s/a1)**(Rational(1, 3)), -(s/a1)**(Rational(1, 3))/2 - sqrt(3)*I*(s/a1)**(Rational(1, 3))/2,
-(s/a1)**(Rational(1, 3))/2 + sqrt(3)*I*(s/a1)**(Rational(1, 3))/2]
assert str(expect3.zeros()) == str([0.125 - 1.11102430216445*sqrt(-0.405063291139241*p**3 - 1.0),
1.11102430216445*sqrt(-0.405063291139241*p**3 - 1.0) + 0.125])
assert tf_.zeros() == [k**(Rational(1, 3)), -k**(Rational(1, 3))/2 - sqrt(3)*I*k**(Rational(1, 3))/2,
-k**(Rational(1, 3))/2 + sqrt(3)*I*k**(Rational(1, 3))/2]
assert _TF.zeros() == [CRootOf(x**9 + x + 1, 0), 0, CRootOf(x**9 + x + 1, 1), CRootOf(x**9 + x + 1, 2),
CRootOf(x**9 + x + 1, 3), CRootOf(x**9 + x + 1, 4), CRootOf(x**9 + x + 1, 5), CRootOf(x**9 + x + 1, 6),
CRootOf(x**9 + x + 1, 7), CRootOf(x**9 + x + 1, 8)]
raises(NotImplementedError, lambda: TransferFunction(a0*x**10 + x + x**2, x**2, x).zeros())
# negation of TF.
tf2 = TransferFunction(s + 3, s**2 - s**3 + 9, s)
tf3 = TransferFunction(-3*p + 3, 1 - p, p)
assert -tf2 == TransferFunction(-s - 3, s**2 - s**3 + 9, s)
assert -tf3 == TransferFunction(3*p - 3, 1 - p, p)
# taking power of a TF.
tf4 = TransferFunction(p + 4, p - 3, p)
tf5 = TransferFunction(s**2 + 1, 1 - s, s)
expect2 = TransferFunction((s**2 + 1)**3, (1 - s)**3, s)
expect1 = TransferFunction((p + 4)**2, (p - 3)**2, p)
assert (tf4*tf4).doit() == tf4**2 == pow(tf4, 2) == expect1
assert (tf5*tf5*tf5).doit() == tf5**3 == pow(tf5, 3) == expect2
assert tf5**0 == pow(tf5, 0) == TransferFunction(1, 1, s)
assert Series(tf4).doit()**-1 == tf4**-1 == pow(tf4, -1) == TransferFunction(p - 3, p + 4, p)
assert (tf5*tf5).doit()**-1 == tf5**-2 == pow(tf5, -2) == TransferFunction((1 - s)**2, (s**2 + 1)**2, s)
raises(ValueError, lambda: tf4**(s**2 + s - 1))
raises(ValueError, lambda: tf5**s)
raises(ValueError, lambda: tf4**tf5)
# sympy's own functions.
tf = TransferFunction(s - 1, s**2 - 2*s + 1, s)
tf6 = TransferFunction(s + p, p**2 - 5, s)
assert factor(tf) == TransferFunction(s - 1, (s - 1)**2, s)
assert tf.num.subs(s, 2) == tf.den.subs(s, 2) == 1
# subs & xreplace
assert tf.subs(s, 2) == TransferFunction(s - 1, s**2 - 2*s + 1, s)
assert tf6.subs(p, 3) == TransferFunction(s + 3, 4, s)
assert tf3.xreplace({p: s}) == TransferFunction(-3*s + 3, 1 - s, s)
raises(TypeError, lambda: tf3.xreplace({p: exp(2)}))
assert tf3.subs(p, exp(2)) == tf3
tf7 = TransferFunction(a0*s**p + a1*p**s, a2*p - s, s)
assert tf7.xreplace({s: k}) == TransferFunction(a0*k**p + a1*p**k, a2*p - k, k)
assert tf7.subs(s, k) == TransferFunction(a0*s**p + a1*p**s, a2*p - s, s)
def test_TransferFunction_functions():
# explicitly cancel poles and zeros.
tf0 = TransferFunction(s**5 + s**3 + s, s - s**2, s)
a = TransferFunction(-(s**4 + s**2 + 1), s - 1, s)
assert tf0.simplify() == simplify(tf0) == a
tf1 = TransferFunction((p + 3)*(p - 1), (p - 1)*(p + 5), p)
b = TransferFunction(p + 3, p + 5, p)
assert tf1.simplify() == simplify(tf1) == b
# expand the numerator and the denominator.
G1 = TransferFunction((1 - s)**2, (s**2 + 1)**2, s)
G2 = TransferFunction(1, -3, p)
c = (a2*s**p + a1*s**s + a0*p**p)*(p**s + s**p)
d = (b0*s**s + b1*p**s)*(b2*s*p + p**p)
e = a0*p**p*p**s + a0*p**p*s**p + a1*p**s*s**s + a1*s**p*s**s + a2*p**s*s**p + a2*s**(2*p)
f = b0*b2*p*s*s**s + b0*p**p*s**s + b1*b2*p*p**s*s + b1*p**p*p**s
g = a1*a2*s*s**p + a1*p*s + a2*b1*p*s*s**p + b1*p**2*s
G3 = TransferFunction(c, d, s)
G4 = TransferFunction(a0*s**s - b0*p**p, (a1*s + b1*s*p)*(a2*s**p + p), p)
assert G1.expand() == TransferFunction(s**2 - 2*s + 1, s**4 + 2*s**2 + 1, s)
assert tf1.expand() == TransferFunction(p**2 + 2*p - 3, p**2 + 4*p - 5, p)
assert G2.expand() == G2
assert G3.expand() == TransferFunction(e, f, s)
assert G4.expand() == TransferFunction(a0*s**s - b0*p**p, g, p)
# purely symbolic polynomials.
p1 = a1*s + a0
p2 = b2*s**2 + b1*s + b0
SP1 = TransferFunction(p1, p2, s)
expect1 = TransferFunction(2.0*s + 1.0, 5.0*s**2 + 4.0*s + 3.0, s)
expect1_ = TransferFunction(2*s + 1, 5*s**2 + 4*s + 3, s)
assert SP1.subs({a0: 1, a1: 2, b0: 3, b1: 4, b2: 5}) == expect1_
assert SP1.subs({a0: 1, a1: 2, b0: 3, b1: 4, b2: 5}).evalf() == expect1
assert expect1_.evalf() == expect1
c1, d0, d1, d2 = symbols('c1, d0:3')
p3, p4 = c1*p, d2*p**3 + d1*p**2 - d0
SP2 = TransferFunction(p3, p4, p)
expect2 = TransferFunction(2.0*p, 5.0*p**3 + 2.0*p**2 - 3.0, p)
expect2_ = TransferFunction(2*p, 5*p**3 + 2*p**2 - 3, p)
assert SP2.subs({c1: 2, d0: 3, d1: 2, d2: 5}) == expect2_
assert SP2.subs({c1: 2, d0: 3, d1: 2, d2: 5}).evalf() == expect2
assert expect2_.evalf() == expect2
SP3 = TransferFunction(a0*p**3 + a1*s**2 - b0*s + b1, a1*s + p, s)
expect3 = TransferFunction(2.0*p**3 + 4.0*s**2 - s + 5.0, p + 4.0*s, s)
expect3_ = TransferFunction(2*p**3 + 4*s**2 - s + 5, p + 4*s, s)
assert SP3.subs({a0: 2, a1: 4, b0: 1, b1: 5}) == expect3_
assert SP3.subs({a0: 2, a1: 4, b0: 1, b1: 5}).evalf() == expect3
assert expect3_.evalf() == expect3
SP4 = TransferFunction(s - a1*p**3, a0*s + p, p)
expect4 = TransferFunction(7.0*p**3 + s, p - s, p)
expect4_ = TransferFunction(7*p**3 + s, p - s, p)
assert SP4.subs({a0: -1, a1: -7}) == expect4_
assert SP4.subs({a0: -1, a1: -7}).evalf() == expect4
assert expect4_.evalf() == expect4
# negation of TF.
tf2 = TransferFunction(s + 3, s**2 - s**3 + 9, s)
tf3 = TransferFunction(-3*p + 3, 1 - p, p)
assert -tf2 == TransferFunction(-s - 3, s**2 - s**3 + 9, s)
assert -tf3 == TransferFunction(3*p - 3, 1 - p, p)
# taking power of a TF.
tf4 = TransferFunction(p + 4, p - 3, p)
tf5 = TransferFunction(s**2 + 1, 1 - s, s)
expect2 = TransferFunction((s**2 + 1)**3, (1 - s)**3, s)
expect1 = TransferFunction((p + 4)**2, (p - 3)**2, p)
assert (tf4*tf4).doit() == tf4**2 == pow(tf4, 2) == expect1
assert (tf5*tf5*tf5).doit() == tf5**3 == pow(tf5, 3) == expect2
assert tf5**0 == pow(tf5, 0) == TransferFunction(1, 1, s)
assert Series(tf4).doit()**-1 == tf4**-1 == pow(tf4, -1) == TransferFunction(p - 3, p + 4, p)
assert (tf5*tf5).doit()**-1 == tf5**-2 == pow(tf5, -2) == TransferFunction((1 - s)**2, (s**2 + 1)**2, s)
raises(ValueError, lambda: tf4**(s**2 + s - 1))
raises(ValueError, lambda: tf5**s)
raises(ValueError, lambda: tf4**tf5)
# sympy's own functions.
tf = TransferFunction(s - 1, s**2 - 2*s + 1, s)
tf6 = TransferFunction(s + p, p**2 - 5, s)
assert factor(tf) == TransferFunction(s - 1, (s - 1)**2, s)
assert tf.num.subs(s, 2) == tf.den.subs(s, 2) == 1
# subs & xreplace
assert tf.subs(s, 2) == TransferFunction(s - 1, s**2 - 2*s + 1, s)
assert tf6.subs(p, 3) == TransferFunction(s + 3, 4, s)
assert tf3.xreplace({p: s}) == TransferFunction(-3*s + 3, 1 - s, s)
raises(TypeError, lambda: tf3.xreplace({p: exp(2)}))
assert tf3.subs(p, exp(2)) == tf3
tf7 = TransferFunction(a0*s**p + a1*p**s, a2*p - s, s)
assert tf7.xreplace({s: k}) == TransferFunction(a0*k**p + a1*p**k, a2*p - k, k)
assert tf7.subs(s, k) == TransferFunction(a0*s**p + a1*p**s, a2*p - s, s)