[PQ] Add unary minus operator

src/blackmisc/pq/physicalquantity.cpp

@@ -237,6 +237,14 @@ namespace BlackMisc
             return copy;
         }
 
+        template <class MU, class PQ>
+        PQ CPhysicalQuantity<MU, PQ>::operator -() const
+        {
+            PQ copy = *derived();
+            copy *= -1;
+            return copy;
+        }
+
         template <class MU, class PQ>
         bool CPhysicalQuantity<MU, PQ>::lessThan(const CPhysicalQuantity<MU, PQ> &other) const
         {

src/blackmisc/pq/physicalquantity.h

@@ -165,6 +165,9 @@ namespace BlackMisc
             //! Operator /
             PQ operator /(double divide) const;
 
+            //! Unary operator -
+            PQ operator -() const;
+
             //! Equal operator ==
             friend bool operator==(const CPhysicalQuantity &a, const CPhysicalQuantity &b) { return a.equals(b); }