Merge pull request #1617 from artpelling/discrete-BT

enable discrete-time BT

AUTHORS.md

@@ -16,7 +16,7 @@
   * several additional features for neural networks
 
 * Art Pelling, a.pelling@tu-berlin.de
-  * support for discrete-time LTI systems and Lyapunov equations
+  * support for discrete-time LTI systems, Lyapunov equations and balanced truncation
   * dedicated Hankel operator class
 
 ### pyMOR 2021.2

src/pymor/reductors/basic.py

@@ -337,7 +337,7 @@ class LTIPGReductor(ProjectionBasedReductor):
         return projected_operators
 
     def build_rom(self, projected_operators, error_estimator):
-        return LTIModel(error_estimator=error_estimator, **projected_operators)
+        return LTIModel(error_estimator=error_estimator, sampling_time=self.fom.sampling_time, **projected_operators)
 
     def extend_basis(self, **kwargs):
         raise NotImplementedError

src/pymor/reductors/bt.py

@@ -136,8 +136,6 @@ class BTReductor(GenericBTReductor):
     """
 
     def _gramians(self):
-        if self.fom.sampling_time > 0:
-            raise NotImplementedError
         return self.fom.gramian('c_lrcf', mu=self.mu), self.fom.gramian('o_lrcf', mu=self.mu)
 
     def error_bounds(self):