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fix discete time simulation time step issue#332 (#356)

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control
- tests
  - timeresp_test.py
- timeresp.py

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+46

-4

lines changed

`‎control/tests/timeresp_test.py`

Lines changed: 39 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -471,6 +471,45 @@ def test_time_vector(self):`
`471`	`471`	`squeeze=False)`
`472`	`472`	`self.assertTrue(isinstance(context.exception,ValueError))`
`473`	`473`
	`474`	`+deftest_discrete_time_steps(self):`
	`475`	`+"""Make sure rounding errors in sample time are handled properly"""`
	`476`	`+# See https://github.com/python-control/python-control/issues/332)`
	`477`	`+#`
	`478`	`+# These tests play around with the input time vector to make sure that`
	`479`	`+# small rounding errors don't generate spurious errors.`
	`480`	`+`
	`481`	`+# Discrete time system to use for simulation`
	`482`	`+# self.siso_dtf2 = TransferFunction([1], [1, 1, 0.25], 0.2)`
	`483`	`+`
	`484`	`+# Set up a time range and simulate`
	`485`	`+T=np.arange(0,100,0.2)`
	`486`	`+tout1,yout1=step_response(self.siso_dtf2,T)`
	`487`	`+`
	`488`	`+# Simulate every other time step`
	`489`	`+T=np.arange(0,100,0.4)`
	`490`	`+tout2,yout2=step_response(self.siso_dtf2,T)`
	`491`	`+np.testing.assert_array_almost_equal(tout1[::2],tout2)`
	`492`	`+np.testing.assert_array_almost_equal(yout1[::2],yout2)`
	`493`	`+`
	`494`	`+# Add a small error into some of the time steps`
	`495`	`+T=np.arange(0,100,0.2)`
	`496`	`+T[1:-2:2]-=1e-12# tweak second value and a few others`
	`497`	`+tout3,yout3=step_response(self.siso_dtf2,T)`
	`498`	`+np.testing.assert_array_almost_equal(tout1,tout3)`
	`499`	`+np.testing.assert_array_almost_equal(yout1,yout3)`
	`500`	`+`
	`501`	`+# Add a small error into some of the time steps (w/ skipping)`
	`502`	`+T=np.arange(0,100,0.4)`
	`503`	`+T[1:-2:2]-=1e-12# tweak second value and a few others`
	`504`	`+tout4,yout4=step_response(self.siso_dtf2,T)`
	`505`	`+np.testing.assert_array_almost_equal(tout2,tout4)`
	`506`	`+np.testing.assert_array_almost_equal(yout2,yout4)`
	`507`	`+`
	`508`	`+# Make sure larger errors do generate an error`
	`509`	`+T=np.arange(0,100,0.2)`
	`510`	`+T[1:-2:2]-=1e-3# change second value and a few others`
	`511`	`+self.assertRaises(ValueError,step_response,self.siso_dtf2,T)`
	`512`	`+`
`474`	`513`	`deftest_time_series_data_convention(self):`
`475`	`514`	`"""Make sure time series data matches documentation conventions"""`
`476`	`515`	`# SISO continuous time`

`‎control/timeresp.py`

Lines changed: 7 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -365,7 +365,8 @@ def forced_response(sys, T=None, U=0., X0=0., transpose=False,`
`365`	`365`	`# Make sure that the time increment is a multiple of sampling time`
`366`	`366`
`367`	`367`	`# First make sure that time increment is bigger than sampling time`
`368`		`-ifdt<sys.dt:`
	`368`	`+# (with allowance for small precision errors)`
	`369`	`+ifdt<sys.dtandnotnp.isclose(dt,sys.dt):`
`369`	`370`	raiseValueError("Time steps ``T`` must match sampling time")
`370`	`371`
`371`	`372`	`# Now check to make sure it is a multiple (with check against`
`@@ -374,19 +375,21 @@ def forced_response(sys, T=None, U=0., X0=0., transpose=False,`
`374`	`375`	`np.isclose(dt%sys.dt,sys.dt)):`
`375`	`376`	raiseValueError("Time steps ``T`` must be multiples of "
`376`	`377`	`"sampling time")`
	`378`	`+sys_dt=sys.dt`
	`379`	`+`
`377`	`380`	`else:`
`378`		`-sys.dt=dt# For unspecified sampling time, use time incr`
	`381`	`+sys_dt=dt# For unspecified sampling time, use time incr`
`379`	`382`
`380`	`383`	`# Discrete time simulation using signal processing toolbox`
`381`		`-dsys= (A,B,C,D,sys.dt)`
	`384`	`+dsys= (A,B,C,D,sys_dt)`
`382`	`385`
`383`	`386`	`# Use signal processing toolbox for the discrete time simulation`
`384`	`387`	`# Transpose the input to match toolbox convention`
`385`	`388`	`tout,yout,xout=sp.signal.dlsim(dsys,np.transpose(U),T,X0)`
`386`	`389`
`387`	`390`	`ifnotinterpolate:`
`388`	`391`	`# If dt is different from sys.dt, resample the output`
`389`		`-inc=int(round(dt/sys.dt))`
	`392`	`+inc=int(round(dt/sys_dt))`
`390`	`393`	`tout=T# Return exact list of time steps`
`391`	`394`	`yout=yout[::inc, :]`
`392`	`395`	`xout=xout[::inc, :]`

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`‎control/tests/timeresp_test.py`

`‎control/timeresp.py`

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