Merge pull request #73 from odlgroup/issue-49__matrix_representation_…

…of_linear_operator

Closes #49

odl/operator/oputils.py

@@ -0,0 +1,118 @@
+# Copyright 2014, 2015 The ODL development group
+#
+# This file is part of ODL.
+#
+# ODL is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# ODL is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with ODL.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Usefull utility functions on discrete spaces (i.e., either Rn/Cn or
+discretized function spaces), for example obtaining a matrix representation of
+an operator. """
+
+# Imports for common Python 2/3 codebase
+from __future__ import print_function, division, absolute_import
+from future import standard_library
+standard_library.install_aliases()
+
+# External
+import numpy as np
+
+# Internal
+from odl.space.base_ntuples import FnBase
+from odl.set.pspace import ProductSpace
+
+
+def matrix_representation(op):
+    """Returns a matrix representation of a linear operator.
+
+    Parameters
+    ----------
+    op : :class:`~odl.Operator`
+        The linear operator of which one wants a matrix representation.
+
+    Returns
+    ----------
+    matrix : `numpy.ndarray`
+        The matrix representation of the operator.
+
+    Notes
+    ----------
+    The algorithm works by letting the operator act on all unit vectors, and
+    stacking the output as a matrix.
+
+    """
+
+    if not op.is_linear:
+        raise ValueError('The operator is not linear')
+
+    if not (isinstance(op.domain, FnBase) or
+            (isinstance(op.domain, ProductSpace) and
+            all(isinstance(spc, FnBase) for spc in op.domain))):
+        raise TypeError('Operator domain {} is not FnBase, nor ProductSpace '
+                        'with only FnBase components'.format(op.domain))
+
+    if not (isinstance(op.range, FnBase) or
+            (isinstance(op.range, ProductSpace) and
+            all(isinstance(spc, FnBase) for spc in op.range))):
+        raise TypeError('Operator range {} is not FnBase, nor ProductSpace '
+                        'with only FnBase components'.format(op.range))
+
+    # Get the size of the range, and handle ProductSpace
+    # Store for reuse in loop
+    op_ran_is_prod_space = isinstance(op.range, ProductSpace)
+    if op_ran_is_prod_space:
+        num_ran = op.range.size
+        n = [ran.size for ran in op.range]
+    else:
+        num_ran = 1
+        n = [op.range.size]
+
+    # Get the size of the domain, and handle ProductSpace
+    # Store for reuse in loop
+    op_dom_is_prod_space = isinstance(op.domain, ProductSpace)
+    if op_dom_is_prod_space:
+        num_dom = op.domain.size
+        m = [dom.size for dom in op.domain]
+    else:
+        num_dom = 1
+        m = [op.domain.size]
+
+    # Generate the matrix
+    matrix = np.zeros([np.sum(n), np.sum(m)])
+    tmp_ran = op.range.element()  # Store for reuse in loop
+    tmp_dom = op.domain.zero()  # Store for reuse in loop
+    index = 0
+    last_i = last_j = 0
+
+    for i in range(num_dom):
+        for j in range(m[i]):
+            if op_dom_is_prod_space:
+                tmp_dom[last_i][last_j] = 0.0
+                tmp_dom[i][j] = 1.0
+            else:
+                tmp_dom[last_j] = 0.0
+                tmp_dom[j] = 1.0
+            op(tmp_dom, out=tmp_ran)
+            if op_ran_is_prod_space:
+                tmp_idx = 0
+                for k in range(num_ran):
+                    matrix[tmp_idx: tmp_idx + op.range[k].size, index] = (
+                        tmp_ran[k])
+                    tmp_idx += op.range[k].size
+            else:
+                matrix[:, index] = tmp_ran.asarray()
+            index += 1
+            last_j = j
+            last_i = i
+
+    return matrix

test/operator/operator_test.py

@@ -30,8 +30,8 @@
 import odl
 from odl import (Operator, OperatorSum, OperatorComp,
                  OperatorLeftScalarMult, OperatorRightScalarMult,
-                 FunctionalLeftVectorMult,
-                 OperatorRightVectorMult)
+                 FunctionalLeftVectorMult, OperatorRightVectorMult,
+                 MatVecOperator)
 from odl.util.testutils import almost_equal, all_almost_equal
 
 
@@ -184,36 +184,14 @@ def test_nonlinear_composition():
         C = OperatorComp(Bop, Aop)
 
 
-class MultiplyOp(Operator):
-
-    """Multiply with matrix.
-    """
-
-    def __init__(self, matrix, domain=None, range=None):
-        domain = (odl.Rn(matrix.shape[1])
-                  if domain is None else domain)
-        range = (odl.Rn(matrix.shape[0])
-                 if range is None else range)
-        self.matrix = matrix
-
-        super().__init__(domain, range, linear=True)
-
-    def _apply(self, rhs, out):
-        np.dot(self.matrix, rhs.data, out=out.data)
-
-    @property
-    def adjoint(self):
-        return MultiplyOp(self.matrix.T, self.range, self.domain)
-
-
 def test_linear_Op():
     # Verify that the multiply op does indeed work as expected
 
     A = np.random.rand(3, 3)
     x = np.random.rand(3)
     out = np.random.rand(3)
 
-    Aop = MultiplyOp(A)
+    Aop = MatVecOperator(A)
     xvec = Aop.domain.element(x)
     outvec = Aop.range.element()
 
@@ -232,7 +210,8 @@ def test_linear_op_nonsquare():
     x = np.random.rand(3)
     out = np.random.rand(4)
 
-    Aop = MultiplyOp(A)
+    Aop = MatVecOperator(A)
+
     xvec = Aop.domain.element(x)
     outvec = Aop.range.element()
 
@@ -250,7 +229,7 @@ def test_linear_adjoint():
     x = np.random.rand(4)
     out = np.random.rand(3)
 
-    Aop = MultiplyOp(A)
+    Aop = MatVecOperator(A)
     xvec = Aop.range.element(x)
     outvec = Aop.domain.element()
 
@@ -269,8 +248,8 @@ def test_linear_addition():
     x = np.random.rand(3)
     y = np.random.rand(4)
 
-    Aop = MultiplyOp(A)
-    Bop = MultiplyOp(B)
+    Aop = MatVecOperator(A)
+    Bop = MatVecOperator(B)
     xvec = Aop.domain.element(x)
     yvec = Aop.range.element(y)
 
@@ -295,7 +274,7 @@ def test_linear_scale():
     x = np.random.rand(3)
     y = np.random.rand(4)
 
-    Aop = MultiplyOp(A)
+    Aop = MatVecOperator(A)
     xvec = Aop.domain.element(x)
     yvec = Aop.range.element(y)
 
@@ -325,7 +304,7 @@ def test_linear_scale():
 def test_linear_right_vector_mult():
     A = np.random.rand(4, 3)
 
-    Aop = MultiplyOp(A)
+    Aop = MatVecOperator(A)
     vec = Aop.domain.element([1, 2, 3])
     x = Aop.domain.element([4, 5, 6])
     y = Aop.range.element([5, 6, 7, 8])
@@ -354,8 +333,8 @@ def test_linear_composition():
     x = np.random.rand(3)
     y = np.random.rand(5)
 
-    Aop = MultiplyOp(A)
-    Bop = MultiplyOp(B)
+    Aop = MatVecOperator(A)
+    Bop = MatVecOperator(B)
     xvec = Bop.domain.element(x)
     yvec = Aop.range.element(y)
 
@@ -372,7 +351,7 @@ def test_type_errors():
     r3 = odl.Rn(3)
     r4 = odl.Rn(4)
 
-    Aop = MultiplyOp(np.random.rand(3, 3))
+    Aop = MatVecOperator(np.random.rand(3, 3))
     r3Vec1 = r3.zero()
     r3Vec2 = r3.zero()
     r4Vec1 = r4.zero()