def time_invariant(self, expr=None):
"""
Check if ``expr`` is time invariant. ``expr`` may be an expression ``e``
explicitly tracked by the FlowGraph or even a generic subexpression
of ``e``. If no ``expr`` is provided, then time invariance of the entire
FlowGraph is assessed.
"""
if expr is None:
return all(self.time_invariant(v) for v in self.values())
if any(q_timedimension(i) for i in expr.free_symbols):
return False
queue = [expr.rhs if expr.is_Equality else expr]
seen = set()
while queue:
item = queue.pop()
temporaries = set()
for i in retrieve_terminals(item):
if i in seen:
# Already inspected, nothing more can be inferred
continue
elif any(
isinstance(j, Dimension) and j.is_Time
for j in i.free_symbols):
# Definitely not time-invariant
return False
elif i in self:
# Go on with the search
temporaries.add(i)
elif isinstance(i, Dimension):
# Go on with the search, as /i/ is not a time dimension
pass
elif not i.base.function.is_TensorFunction:
# It didn't come from the outside and it's not in self, so
# cannot determine if time-invariant; assume time-varying
return False
seen.add(i)
queue.extend([self[i].rhs for i in temporaries])
return True
def time_invariant(self, expr=None):
"""
Check if ``expr`` is time invariant. ``expr`` may be an expression ``e``
explicitly tracked by the FlowGraph or even a generic subexpression
of ``e``. If no ``expr`` is provided, then time invariance of the entire
FlowGraph is assessed.
"""
if expr is None:
return all(self.time_invariant(v) for v in self.values())
if any(q_timedimension(i) for i in expr.free_symbols):
return False
queue = [expr.rhs if expr.is_Equality else expr]
seen = set()
while queue:
item = queue.pop()
nodes = set()
for i in retrieve_terminals(item):
if i in seen:
# Already inspected, nothing more can be inferred
continue
elif any(isinstance(j, Dimension) and j.is_Time for j in i.free_symbols):
# Definitely not time-invariant
return False
elif i in self:
# Go on with the search
nodes.add(i)
elif isinstance(i, Dimension):
# Go on with the search, as /i/ is not a time dimension
pass
elif not i.function.is_DiscreteFunction:
# It didn't come from the outside and it's not in self, so
# cannot determine if time-invariant; assume time-varying
return False
seen.add(i)
queue.extend([self[i].rhs for i in nodes])
return True