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Commit8c9e807

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committed
discard zero imaginary part for sys.dcgain()
1 parentb41574f commit8c9e807

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6 files changed

+48
-24
lines changed

6 files changed

+48
-24
lines changed

‎control/lti.py

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -208,6 +208,13 @@ def dcgain(self):
208208
raiseNotImplementedError("dcgain not implemented for %s objects"%
209209
str(self.__class__))
210210

211+
def_dcgain(self,warn_infinite):
212+
zeroresp=self(0ifself.isctime()else1,
213+
warn_infinite=warn_infinite)
214+
ifnp.all(np.logical_or(np.isreal(zeroresp),np.isnan(zeroresp.imag))):
215+
returnzeroresp.real
216+
else:
217+
returnzeroresp
211218

212219
# Test to see if a system is SISO
213220
defissiso(sys,strict=False):

‎control/statesp.py

Lines changed: 18 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1216,16 +1216,27 @@ def dcgain(self, warn_infinite=False):
12161216
12171217
.. math: G(1) = C (I - A)^{-1} B + D
12181218
1219+
Parameters
1220+
----------
1221+
warn_infinite : bool, optional
1222+
By default, don't issue a warning message if the zero-frequency
1223+
gain is infinite. Setting `warn_infinite` to generate the warning
1224+
message.
1225+
12191226
Returns
12201227
-------
1221-
gain : ndarray
1222-
An array of shape (outputs,inputs); the array will either be the
1223-
zero-frequency (or DC) gain, or, if the frequency response is
1224-
singular, the array will be filled with (inf + nanj).
1225-
1228+
gain : (outputs, inputs) ndarray or scalar
1229+
Array or scalar value for SISO systems, depending on
1230+
config.defaults['control.squeeze_frequency_response'].
1231+
The value of the array elements or the scalar is either the
1232+
zero-frequency (or DC) gain, or `inf`, if the frequency response
1233+
is singular.
1234+
1235+
For real valued systems, the empty imaginary part of the
1236+
complex zero-frequency response is discarded and a real array or
1237+
scalar is returned.
12261238
"""
1227-
returnself(0,warn_infinite=warn_infinite)ifself.isctime() \
1228-
elseself(1,warn_infinite=warn_infinite)
1239+
returnself._dcgain(warn_infinite)
12291240

12301241
def_isstatic(self):
12311242
"""True if and only if the system has no dynamics, that is,

‎control/tests/freqresp_test.py

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -423,7 +423,7 @@ def test_dcgain_consistency():
423423
sys_ss=ctrl.tf2ss(sys_tf)
424424
assert0insys_ss.pole()
425425

426-
# Finite (real) numerator over 0 denominator => inf + nanj
426+
# Finite (real) numerator over 0 denominator => inf
427427
np.testing.assert_equal(
428428
sys_tf(0,warn_infinite=False),complex(np.inf,np.nan))
429429
np.testing.assert_equal(
@@ -433,9 +433,9 @@ def test_dcgain_consistency():
433433
np.testing.assert_equal(
434434
sys_ss(0j,warn_infinite=False),complex(np.inf,np.nan))
435435
np.testing.assert_equal(
436-
sys_tf.dcgain(warn_infinite=False),complex(np.inf,np.nan))
436+
sys_tf.dcgain(warn_infinite=False),np.inf)
437437
np.testing.assert_equal(
438-
sys_ss.dcgain(warn_infinite=False),complex(np.inf,np.nan))
438+
sys_ss.dcgain(warn_infinite=False),np.inf)
439439

440440
# Set up transfer function with pole, zero at the origin
441441
sys_tf=ctrl.tf([1,0], [1,0])
@@ -448,7 +448,7 @@ def test_dcgain_consistency():
448448
np.testing.assert_equal(
449449
sys_tf(0j,warn_infinite=False),complex(np.nan,np.nan))
450450
np.testing.assert_equal(
451-
sys_tf.dcgain(warn_infinite=False),complex(np.nan,np.nan))
451+
sys_tf.dcgain(warn_infinite=False),np.nan)
452452

453453
# Set up state space version
454454
sys_ss=ctrl.tf2ss(ctrl.tf([1,0], [1,1]))* \
@@ -462,15 +462,15 @@ def test_dcgain_consistency():
462462
np.testing.assert_equal(
463463
sys_ss(0j,warn_infinite=False),complex(np.nan,np.nan))
464464
np.testing.assert_equal(
465-
sys_ss.dcgain(warn_infinite=False),complex(np.nan,np.nan))
465+
sys_ss.dcgain(warn_infinite=False),np.nan)
466466
elif0insys_ss.pole():
467467
# Pole at the origin, but zero elsewhere => should get (inf + nanj)
468468
np.testing.assert_equal(
469469
sys_ss(0,warn_infinite=False),complex(np.inf,np.nan))
470470
np.testing.assert_equal(
471471
sys_ss(0j,warn_infinite=False),complex(np.inf,np.nan))
472472
np.testing.assert_equal(
473-
sys_ss.dcgain(warn_infinite=False),complex(np.inf,np.nan))
473+
sys_ss.dcgain(warn_infinite=False),np.inf)
474474
else:
475475
# Near pole/zero cancellation => nothing sensible to check
476476
pass

‎control/tests/statesp_test.py

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -498,7 +498,7 @@ def test_dc_gain_cont(self):
498498
np.testing.assert_allclose(sys2.dcgain(),expected)
499499

500500
sys3=StateSpace(0.,1.,1.,0.)
501-
np.testing.assert_equal(sys3.dcgain(),complex(np.inf,np.nan))
501+
np.testing.assert_equal(sys3.dcgain(),np.inf)
502502

503503
deftest_dc_gain_discr(self):
504504
"""Test DC gain for discrete-time state-space systems."""
@@ -516,7 +516,7 @@ def test_dc_gain_discr(self):
516516

517517
# summer
518518
sys=StateSpace(1,1,1,0,True)
519-
np.testing.assert_equal(sys.dcgain(),complex(np.inf,np.nan))
519+
np.testing.assert_equal(sys.dcgain(),np.inf)
520520

521521
@pytest.mark.parametrize("outputs",range(1,6))
522522
@pytest.mark.parametrize("inputs",range(1,6))
@@ -539,7 +539,7 @@ def test_dc_gain_integrator(self, outputs, inputs, dt):
539539
c=np.eye(max(outputs,states))[:outputs, :states]
540540
d=np.zeros((outputs,inputs))
541541
sys=StateSpace(a,b,c,d,dt)
542-
dc=np.full_like(d,complex(np.inf,np.nan),dtype=complex)
542+
dc=np.full_like(d,np.inf,dtype=float)
543543
ifsys.issiso():
544544
dc=dc.squeeze()
545545

@@ -953,4 +953,3 @@ def test_xferfcn_ndarray_precedence(op, tf, arr):
953953
ss=ct.tf2ss(tf)
954954
result=op(arr,ss)
955955
assertisinstance(result,ct.StateSpace)
956-

‎control/tests/xferfcn_test.py

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -807,7 +807,7 @@ def test_dcgain_cont(self):
807807
np.testing.assert_equal(sys2.dcgain(),2)
808808

809809
sys3=TransferFunction(6, [1,0])
810-
np.testing.assert_equal(sys3.dcgain(),complex(np.inf,np.nan))
810+
np.testing.assert_equal(sys3.dcgain(),np.inf)
811811

812812
num= [[[15], [21], [33]], [[10], [14], [22]]]
813813
den= [[[1,3], [2,3], [3,3]], [[1,5], [2,7], [3,11]]]
@@ -827,13 +827,13 @@ def test_dcgain_discr(self):
827827

828828
# differencer
829829
sys=TransferFunction(1, [1,-1],True)
830-
np.testing.assert_equal(sys.dcgain(),complex(np.inf,np.nan))
830+
np.testing.assert_equal(sys.dcgain(),np.inf)
831831

832832
# differencer, with warning
833833
sys=TransferFunction(1, [1,-1],True)
834834
withpytest.warns(RuntimeWarning,match="divide by zero"):
835835
np.testing.assert_equal(
836-
sys.dcgain(warn_infinite=True),complex(np.inf,np.nan))
836+
sys.dcgain(warn_infinite=True),np.inf)
837837

838838
# summer
839839
sys=TransferFunction([1,-1], [1],True)

‎control/xferfcn.py

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1070,12 +1070,19 @@ def dcgain(self, warn_infinite=False):
10701070
10711071
Returns
10721072
-------
1073-
gain : ndarray
1074-
The zero-frequency gain
1073+
gain : (outputs, inputs) ndarray or scalar
1074+
Array or scalar value for SISO systems, depending on
1075+
config.defaults['control.squeeze_frequency_response'].
1076+
The value of the array elements or the scalar is either the
1077+
zero-frequency (or DC) gain, or `inf`, if the frequency response
1078+
is singular.
1079+
1080+
For real valued systems, the empty imaginary part of the
1081+
complex zero-frequency response is discarded and a real array or
1082+
scalar is returned.
10751083
10761084
"""
1077-
returnself(0,warn_infinite=warn_infinite)ifself.isctime() \
1078-
elseself(1,warn_infinite=warn_infinite)
1085+
returnself._dcgain(warn_infinite)
10791086

10801087
def_isstatic(self):
10811088
"""returns True if and only if all of the numerator and denominator

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