@@ -186,16 +186,30 @@ def test_nyquist_indent():
186186# FBS Figure 10.10
187187s = ct .tf ('s' )
188188sys = 3 * (s + 6 )** 2 / (s * (s + 1 )** 2 )
189+ # poles: [-1, -1, 0]
189190
190191plt .figure ();
191192count = ct .nyquist_plot (sys )
192193plt .title ("Pole at origin; indent_radius=default" )
193194assert _Z (sys )== count + _P (sys )
194195
196+ # first value of default omega vector was 0.1, replaced by 0. for contour
197+ # indent_radius is larger than 0.1 -> no extra quater circle around origin
198+ count ,contour = ct .nyquist_plot (sys ,plot = False ,indent_radius = .1007 ,
199+ return_contour = True )
200+ np .testing .assert_allclose (contour [0 ],.1007 + 0.j )
201+ # second value of omega_vector is larger than indent_radius: not indented
202+ assert np .all (contour .real [2 :]== 0. )
203+
195204plt .figure ();
196- count = ct .nyquist_plot (sys ,indent_radius = 0.01 )
205+ count ,contour = ct .nyquist_plot (sys ,indent_radius = 0.01 ,
206+ return_contour = True )
197207plt .title ("Pole at origin; indent_radius=0.01; encirclements = %d" % count )
198208assert _Z (sys )== count + _P (sys )
209+ # indent radius is smaller than the start of the default omega vector
210+ # check that a quarter circle around the pole at origin has been added.
211+ np .testing .assert_allclose (contour [:50 ].real ** 2 + contour [:50 ].imag ** 2 ,
212+ 0.01 ** 2 )
199213
200214plt .figure ();
201215count = ct .nyquist_plot (sys ,indent_direction = 'left' )