From c0d7b6e03fc2abf420c8e2c4bce9ad3ddc1db0fc Mon Sep 17 00:00:00 2001
From: Max Kahnt <max.kahnt@fu-berlin.de>
Date: Tue, 3 Oct 2017 15:53:07 +0200
Subject: [PATCH] Add getScalar to extract the scale factor of some scaling.
---
dune/matrix-vector/CMakeLists.txt | 3 +-
dune/matrix-vector/getscalar.hh | 83 +++++++++++++++++++++++++++++++
2 files changed, 85 insertions(+), 1 deletion(-)
create mode 100644 dune/matrix-vector/getscalar.hh
diff --git a/dune/matrix-vector/CMakeLists.txt b/dune/matrix-vector/CMakeLists.txt
index 9e4da1f..c1f8cb1 100644
--- a/dune/matrix-vector/CMakeLists.txt
+++ b/dune/matrix-vector/CMakeLists.txt
@@ -1,4 +1,4 @@
-add_subdirectory(test)
+add_subdirectory(test)
add_subdirectory(traits)
#install headers
@@ -12,6 +12,7 @@ install(FILES
concepts.hh
crossproduct.hh
genericvectortools.hh
+ getscalar.hh
ldlt.hh
promote.hh
singlenonzerocolumnmatrix.hh
diff --git a/dune/matrix-vector/getscalar.hh b/dune/matrix-vector/getscalar.hh
new file mode 100644
index 0000000..608042c
--- /dev/null
+++ b/dune/matrix-vector/getscalar.hh
@@ -0,0 +1,83 @@
+#ifndef DUNE_MATRIX_VECTOR_GETSCALAR_HH
+#define DUNE_MATRIX_VECTOR_GETSCALAR_HH
+
+#include <utility>
+
+#include <dune/common/fmatrix.hh>
+#include <dune/istl/scaledidmatrix.hh>
+
+#include <dune/matrix-vector/traits/utilities.hh>
+
+namespace Dune {
+namespace MatrixVector {
+
+template <class, class Enable = void>
+struct Helper;
+
+/**
+ * \brief Extract the scalar of some scale provider.
+ * \param tol Is the acceptable difference for ambiguous extracted scalings.
+ **/
+template <class Scalar, class Provider>
+static Scalar getScalar(Provider&& p, Scalar tol = 0.0) {
+ static_assert(isScalar<Scalar>(), "Type not know as scalar.");
+
+ return Helper<std::decay_t<Provider>>::template get<Scalar>(
+ std::forward<Provider>(p), tol);
+}
+
+//! \brief If the scaling is given by a scalar, that is what we return.
+template <class Provider>
+struct Helper<Provider, EnableScalar<Provider>> {
+ template <class Scalar, class Provider_>
+ static Scalar get(Provider_&& p, Scalar) {
+ return p;
+ }
+};
+
+//! \brief If the scaling is given by a matrix a*Id, extract a.
+//! Fail if given matrix is not a multiple of Id.
+template <class Provider>
+struct Helper<Provider, EnableMatrix<Provider>> {
+ template <class Scalar, class K, int n>
+ static Scalar get(const ScaledIdentityMatrix<K, n>& m, Scalar) {
+ return m.scalar();
+ }
+
+ template <class Scalar, class K, int n>
+ static Scalar get(const FieldMatrix<K, n, n>& m, Scalar tol) {
+ // TODO make istl-with-checking like mechanism where one avoids all
+ // the following computations and just returns the first value.
+
+ using namespace std;
+ Scalar result_min = std::numeric_limits<Scalar>::infinity();
+ Scalar result_max = -std::numeric_limits<Scalar>::infinity();
+ Scalar others_max = 0;
+ for (size_t i = 0; i < n; ++i) {
+ for (size_t j = 0; j < n; ++j) {
+ if (i == j) {
+ result_min = min(result_min, m[i][j]);
+ result_max = max(result_max, m[i][j]);
+ } else {
+ others_max = max(others_max, fabs(m[i][j]));
+ }
+ }
+ }
+ if(others_max > tol)
+ DUNE_THROW(Exception, "Offdiagonal is not (close enought to) zero.");
+ if(fabs(result_max - result_min) > tol)
+ DUNE_THROW(Exception, "Diagonal scaling is (too) ambiguous.");
+ return result_max;
+ }
+
+ template <class Scalar, class M>
+ static Scalar get(const M&, Scalar) {
+ static_assert(AlwaysFalse<M>::value, "Not yet implemented.");
+ return 1.0;
+ }
+};
+
+} // end namespace MatrixVector
+} // end namespace Dune
+
+#endif // DUNE_MATRIX_VECTOR_GETSCALAR_HH
--
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