speed up calaculation of particle properties

calculations of particle properties may now be done already inside the
SingleSpeciesAnalyzer class. Calculations of particle properties which
require scalar values on a per species basis (usually mass and charge)
will speed up, because these constant values will not be repeated
using np.repeat before the calculation.
Timed on Laptop with 10e6 particles (timit package, 20 repetitions):
calculating gamma        0.43 --> 0.245 sec (57%)
calculating Ekin_MeV_qm  0.90 --> 0.36  sec (40%)

postpic/analyzer/particles.py

@@ -160,7 +160,42 @@ def __len__(self):  # = number of particles
     # the following functions can be computed more efficiently here
     # than in the ParticleAnalyzer.
     # (example: if mass is constant for the entire species, it doesnt
-    # have to be expanded using np.repeat before the calculation)
+    # have to be repeated using np.repeat before the calculation)
+
+    def gamma(self):
+        return np.sqrt(1 +
+                       (self.Px() ** 2 + self.Py() ** 2 + self.Pz() ** 2)
+                       / (self.mass() * pc.c) ** 2)
+
+    def mass_u(self):
+        return self.mass() / pc.mass_u
+
+    def charge_e(self):
+        return self.charge() / pc.qe
+
+    def Eruhe(self):
+        return self.mass() * pc.c ** 2
+
+    def Ekin(self):
+        return (self.gamma() - 1) * self.Eruhe()
+
+    def Ekin_MeV(self):
+        return self.Ekin() / pc.qe / 1e6
+
+    def Ekin_MeV_amu(self):
+        return self.Ekin_MeV() / self.mass_u()
+
+    def Ekin_MeV_qm(self):
+        return self.Ekin_MeV() * self.charge_e() / self.mass_u()
+
+    def Ekin_keV(self):
+        return self.Ekin() / pc.qe / 1e3
+
+    def Ekin_keV_amu(self):
+        return self.Ekin_keV() / self.mass_u()
+
+    def Ekin_keV_qm(self):
+        return self.Ekin_MeV() * self.charge_e() / self.mass_u()
 
 
 class ParticleAnalyzer(object):
@@ -340,6 +375,11 @@ def getcompresslog(self):
     # --- map functions to SingleSpeciesAnalyzer
 
     def _map2ssa(self, func):
+        '''
+        maps a function to the SingleSpeciesAnalyzers. If the SingleSpeciesAnalyzer
+        returns a single scalar, it will be repeated using np.repeat to ensure
+        that a list will always be returned.
+        '''
         ret = np.array([])
         for ssa in self._ssas:
             a = getattr(ssa, func)()
@@ -365,7 +405,7 @@ def mass(self):  # SI
     mass.name = 'm'
 
     def mass_u(self):
-        return self.mass() / pc.mass_u
+        return self._mass2ssa('mass_u')
     mass_u.unit = 'u'
     mass_u.name = 'm'
 
@@ -375,12 +415,12 @@ def charge(self):  # SI
     charge.name = 'q'
 
     def charge_e(self):
-        return self.charge() / pc.qe
+        return self._map2ssa('charge_e')
     charge.unit = 'qe'
     charge.name = 'q'
 
     def Eruhe(self):
-        return self.mass() * pc.c ** 2
+        return self._map2ssa('Eruhe')
 
     def Px(self):
         return self._map2ssa('Px')
@@ -443,44 +483,42 @@ def V(self):
     V.name = 'V'
 
     def gamma(self):
-        return np.sqrt(1 +
-                       (self.Px() ** 2 + self.Py() ** 2 + self.Pz() ** 2)
-                       / (self.mass() * pc.c) ** 2)
+        return self._map2ssa('gamma')
     gamma.unit = r'$\gamma$'
     gamma.name = 'gamma'
 
     def Ekin(self):
-        return (self.gamma() - 1) * self.Eruhe()
+        return self._map2ssa('Ekin')
     Ekin.unit = 'J'
     Ekin.name = 'Ekin'
 
     def Ekin_MeV(self):
-        return self.Ekin() / pc.qe / 1e6
+        return self._map2ssa('Ekin_MeV')
     Ekin_MeV.unit = 'MeV'
     Ekin_MeV.name = 'Ekin'
 
     def Ekin_MeV_amu(self):
-        return self.Ekin_MeV() / self.mass_u()
+        return self._map2ssa('Ekin_MeV_amu')
     Ekin_MeV_amu.unit = 'MeV / amu'
     Ekin_MeV_amu.name = 'Ekin / amu'
 
     def Ekin_MeV_qm(self):
-        return self.Ekin_MeV() * self.charge_e() / self.mass_u()
+        return self._map2ssa('Ekin_MeV_qm')
     Ekin_MeV_qm.unit = 'MeV*q/m'
     Ekin_MeV_qm.name = 'Ekin * q/m'
 
     def Ekin_keV(self):
-        return self.Ekin() / pc.qe / 1e3
+        return self._map2ssa('Ekin_keV')
     Ekin_keV.unit = 'keV'
     Ekin_keV.name = 'Ekin'
 
     def Ekin_keV_amu(self):
-        return self.Ekin_keV() / self.mass_u()
+        return self._map2ssa('Ekin_keV_amu')
     Ekin_keV_amu.unit = 'keV / amu'
     Ekin_keV_amu.name = 'Ekin / amu'
 
     def Ekin_keV_qm(self):
-        return self.Ekin_MeV() * self.charge_e() / self.mass_u()
+        return self._map2ssa('Ekin_keV_qm')
     Ekin_keV_qm.unit = 'keV*q/m'
     Ekin_keV_qm.name = 'Ekin * q/m'