Matrix-Free Linear Operator

psydac/linalg/basic.py

@@ -11,6 +11,7 @@
 
 import numpy as np
 from scipy.sparse import coo_matrix
+from types import LambdaType 
 
 from psydac.utilities.utils import is_real
 
@@ -25,7 +26,8 @@
     'ComposedLinearOperator',
     'PowerLinearOperator',
     'InverseLinearOperator',
-    'LinearSolver'
+    'LinearSolver',
+    'MatrixFreeLinearOperator'
 )
 
 #===============================================================================
@@ -1111,3 +1113,52 @@ def solve(self, rhs, out=None):
     @property
     def T(self):
         return self.transpose()
+
+#===============================================================================
+class MatrixFreeLinearOperator(LinearOperator):
+    """
+    General operator acting between two vector spaces V and W. It only requires a callable dot method.
+
+    """
+
+    def __init__(self, domain, codomain, dot):
+
+        assert isinstance(domain, VectorSpace)
+        assert isinstance(codomain, VectorSpace)       
+        assert isinstance(dot, LambdaType)
+
+        self._domain = domain
+        self._codomain = codomain
+        self._dot = dot
+
+    @property
+    def domain(self):
+        return self._domain
+
+    @property
+    def codomain(self):
+        return self._codomain
+
+    @property
+    def dtype(self):
+        return None
+
+    def dot(self, v, out=None):
+        assert isinstance(v, Vector)
+        assert v.space == self.domain
+
+        if out is not None:
+            assert isinstance(out, Vector)
+            assert out.space == self.codomain
+
+        return self._dot(v, out=out)
+
+    def toarray(self):
+        raise NotImplementedError('toarray() is not defined for MatrixFreeLinearOperator.')
+
+    def tosparse(self):
+        raise NotImplementedError('tosparse() is not defined for MatrixFreeLinearOperator.')
+
+    def transpose(self):
+        raise NotImplementedError('transpose() is not defined for MatrixFreeLinearOperator.')
+