Added getPeriodicBoxVolume() to State

openmmapi/include/openmm/State.h

@@ -99,6 +99,10 @@ public:
      * @param c      on exit, this contains the vector defining the third edge of the periodic box
      */
     void getPeriodicBoxVectors(Vec3& a, Vec3& b, Vec3& c) const;
+    /**
+     * Get the volume of the periodic box (measured in nm^3).
+     */
+    double getPeriodicBoxVolume() const;
     /**
      * Get a map containing the values of all parameters.  If this State does not contain parameters, this will throw an exception.
      */

openmmapi/src/State.cpp

@@ -68,6 +68,9 @@ void State::getPeriodicBoxVectors(Vec3& a, Vec3& b, Vec3& c) const {
     b = periodicBoxVectors[1];
     c = periodicBoxVectors[2];
 }
+double State::getPeriodicBoxVolume() const {
+    return periodicBoxVectors[0].dot(periodicBoxVectors[1].cross(periodicBoxVectors[2]));
+}
 const map<string, double>& State::getParameters() const {
     if ((types&Parameters) == 0)
         throw OpenMMException("Invoked getParameters() on a State which does not contain parameters.");

wrappers/python/src/swig_doxygen/swig_lib/python/pythoncode.i

@@ -10,6 +10,7 @@ RMIN_PER_SIGMA=math.pow(2, 1/6.0)
 RVDW_PER_SIGMA=math.pow(2, 1/6.0)/2.0
 
 import simtk.unit as unit
+from simtk.openmm.vec3 import Vec3
 
 class State(_object):
     """
@@ -103,6 +104,14 @@ class State(_object):
         returnValue = unit.Quantity(returnValue, unit.nanometers)
         return returnValue
     
+    def getPeriodicBoxVolume(self):
+        """Get the volume of the periodic box."""
+        a = self._periodicBoxVectorsList[0]
+        b = self._periodicBoxVectorsList[1]
+        c = self._periodicBoxVectorsList[2]
+        bcrossc = Vec3(b[1]*c[2]-b[2]*c[1], b[2]*c[0]-b[0]*c[2], b[0]*c[1]-b[1]*c[0])
+        return unit.Quantity(unit.dot(a, bcrossc), unit.nanometers*unit.nanometers*unit.nanometers)
+
     def getPositions(self, asNumpy=False):
         """Get the position of each particle with units.
            Raises an exception if postions where not requested in