make certain that the vector storage and the size_vector variable are consistent in computes

src/compute_pressure.cpp

@@ -101,7 +101,7 @@ ComputePressure::ComputePressure(LAMMPS *lmp, int narg, char **arg) :
     error->all(FLERR,"Compute pressure requires temperature ID "
                "to include kinetic energy");
 
-  vector = new double[6];
+  vector = new double[size_vector];
   nvirial = 0;
   vptr = NULL;
 }