Merge branch 'feature/interval-multiplication' into 'master'

Interval: scalar multiplication

See merge request !49

dune/solvers/common/interval.hh

@@ -57,6 +57,15 @@ public:
       return *this;
     }
 
+    /** \brief Scalar multiplication
+     */
+    Interval& operator*=(const field_type& c)
+    {
+      data_[0] *= c;
+      data_[1] *= c;
+      return *this;
+    }
+
     /** \brief Project a scalar onto the interval
      */
     field_type projectIn(const field_type& x) const
@@ -97,6 +106,22 @@ private:
     std::array<field_type,2> data_;
 };
 
+
+//! Scalar multiplication from the left
+template <class field_type>
+Interval<field_type> operator*(const field_type& c, const Interval<field_type>& i)
+{
+  auto ret = i;
+  return ret *= c;
+}
+
+//! Scalar multiplication from the right
+template <class field_type>
+Interval<field_type> operator*(const Interval<field_type>& i, const field_type& c)
+{
+  return c * i;
+}
+
 //! Output operator for Interval
 template <class field_type>
 inline std::ostream& operator<< (std::ostream& s, const Interval<field_type>& interval)