replace extent in weighting and displacement

store extent value in n_particles

examples/9_particle_write_serial.py

@@ -16,7 +16,7 @@
 if __name__ == "__main__":
     # open file for writing
     f = Series(
-        "../samples/7_particle_write_serial_py.h5",
+        "../samples/9_particle_write_serial_py.h5",
         Access.create
     )
 
@@ -35,25 +35,29 @@
         "Electrons... the necessary evil for ion acceleration! ",
         "Just kidding.")
 
+    n_particles = 234
+
     # let's set a weird user-defined record this time
     electrons["displacement"].unit_dimension = {Unit_Dimension.M: 1}
     electrons["displacement"][SCALAR].unit_SI = 1.e-6
-    dset = Dataset(np.dtype("float64"), extent=[2])
+    dset = Dataset(np.dtype("float64"), extent=[n_particles])
     electrons["displacement"][SCALAR].reset_dataset(dset)
     electrons["displacement"][SCALAR].make_constant(42.43)
     # don't like it anymore? remove it with:
     # del electrons["displacement"]
 
-    electrons["weighting"][SCALAR].make_constant(1.e-5)
+    electrons["weighting"][SCALAR] \
+        .reset_dataset(Dataset(np.dtype("float32"), extent=[n_particles])) \
+        .make_constant(1.e-5)
 
-    particlePos_x = np.random.rand(234).astype(np.float32)
-    particlePos_y = np.random.rand(234).astype(np.float32)
+    particlePos_x = np.random.rand(n_particles).astype(np.float32)
+    particlePos_y = np.random.rand(n_particles).astype(np.float32)
     d = Dataset(particlePos_x.dtype, extent=particlePos_x.shape)
     electrons["position"]["x"].reset_dataset(d)
     electrons["position"]["y"].reset_dataset(d)
 
-    particleOff_x = np.arange(234, dtype=np.uint)
-    particleOff_y = np.arange(234, dtype=np.uint)
+    particleOff_x = np.arange(n_particles, dtype=np.uint)
+    particleOff_y = np.arange(n_particles, dtype=np.uint)
     d = Dataset(particleOff_x.dtype, particleOff_x.shape)
     electrons["positionOffset"]["x"].reset_dataset(d)
     electrons["positionOffset"]["y"].reset_dataset(d)