Added clean_tf() function

ldriever · ldriever · commit d3aaafb3133b · 2020-07-26T12:51:00.000+02:00
Added the clean_tf() function at the bottom of xferfcn.py, adjusting it slightly to be conform with the existing imports in the file and adding one import from another file of the control library. Also adjusted the documentation for the function to match the existing style. Additionally fixed a formatting error in the documentation for clean_ss()
diff --git a/control/statesp.py b/control/statesp.py
@@ -1515,12 +1515,12 @@ def clean_ss(sys, precision=10):
     ----------
     sys : LTI (StateSpace, or TransferFunction)
         LTI system whose data will be returned
-    precision: integer
+    precision : integer
         Number of decimals to be left unchanged in rounding
 
     Returns
     -------
-    out: StateSpace
+    out : StateSpace
         LTI StateSpace rounded to the desired precision
 
     Raises
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -63,6 +63,7 @@
 from itertools import chain
 from re import sub
 from .lti import LTI, timebaseEqual, timebase, isdtime
+from .statesp import StateSpace
 from . import config
 
 __all__ = ['TransferFunction', 'tf', 'ss2tf', 'tfdata']
@@ -1565,6 +1566,56 @@ def _clean_part(data):
     return data
 
 
+def clean_tf(sys, input=None, output=None, precision=10):
+    """
+    Rounds the elements of the desired transfer function. This removes small non-zero numbers that, for instance, are
+    a result of computational errors and can otherwise lead to problems. The function also removes cancelling poles
+    and zeros, similar to the control.minreal() function
+
+    Parameters
+    ----------
+    sys : LTI (StateSpace, or TransferFunction)
+        LTI system whose data will be returned
+    input : None
+        optionally an integer referring to the requested input (starting from 1)
+    output : None
+        optionally an integer referring to the requested output (starting from 1)
+    precision : integer
+        Number of decimals to be left unchanged in rounding
+
+    Returns
+    -------
+    out : TransferFunctino
+        LTI TransferFunction rounded to the desired precision
+
+    Raises
+    ------
+    TypeError
+        if sys is not a StateSpace or TransferFunction object
+    """
+    if (type(sys) is not TransferFunction) and (type(sys) is not StateSpace):
+        raise Exception("Neither a StateSpace nor TransferFunction was passed to 'sys'")
+
+    sys = tf(sys).minreal()
+    if input is not None and output is not None:
+        sys = sys[output - 1, input - 1]
+    elif output is not None:
+        sys = sys[output - 1, :]
+    elif input is not None:
+        sys = sys[:, input - 1]
+    num = np.round(sys.num, precision)
+    den = np.round(sys.den, precision)
+    for i in range(sys.outputs):
+        for j in range(sys.inputs):
+            test = True
+            while test:
+                if num[i][j][-1] == den[i][j][-1] == 0:
+                    num[i][j] = np.insert(num[i][j][:-1],0,0)
+                    den[i][j] = np.insert(den[i][j][:-1],0,0)
+                else: test = False
+    return tf(num,den)
+
+
 # Define constants to represent differentiation, unit delay
 TransferFunction.s = TransferFunction([1, 0], [1], 0)
 TransferFunction.z = TransferFunction([1, 0], [1], True)
