init xindices in Euler1DSolver

modmesh/app/euler1d.py

@@ -743,29 +743,30 @@ def update_lines(self):
         :return: None
         """
         if self.use_grid_layout:
+            _s = self.st.svr.xindices
             self.density.update(
                 adata=self.st.density_field,
-                ndata=self.st.svr.density[self.st.svr.xindices]
+                ndata=self.st.svr.density[_s]
             )
             self.pressure.update(
                 adata=self.st.pressure_field,
-                ndata=self.st.svr.pressure[self.st.svr.xindices]
+                ndata=self.st.svr.pressure[_s]
             )
             self.velocity.update(
                 adata=self.st.velocity_field,
-                ndata=self.st.svr.velocity[self.st.svr.xindices]
+                ndata=self.st.svr.velocity[_s]
             )
             self.temperature.update(
                 adata=self.st.temperature_field,
-                ndata=self.st.svr.temperature[self.st.svr.xindices]
+                ndata=self.st.svr.temperature[_s]
             )
             self.internal_energy.update(
                 adata=(self.st.internal_energy_field),
-                ndata=(self.st.svr.internal_energy[self.st.svr.xindices])
+                ndata=(self.st.svr.internal_energy[_s])
             )
             self.entropy.update(
                 adata=self.st.entropy_field,
-                ndata=self.st.svr.entropy[self.st.svr.xindices]
+                ndata=self.st.svr.entropy[_s]
             )
         else:
             for name, is_selected, *_ in self.plot_config.state:

modmesh/onedim/euler1d.py

@@ -24,10 +24,15 @@ class Euler1DSolver:
     method.
     """
 
-    def __init__(self, xmin, xmax, ncoord, time_increment=0.05):
+    def __init__(self, xmin, xmax, ncoord, time_increment=0.05, keep_edge=False):
         self._core = self.init_solver(xmin, xmax, ncoord, time_increment,
                                       gamma=1.4)
         # gamma is 1.4 for air.
+        _ = self.ncoord - 1
+        start = 0 if keep_edge else 2
+        stop = _ if keep_edge else (_ - 2)
+        num = (stop - start) // 2 + 1
+        self.xindices = np.linspace(start, stop, num, dtype='int32')
 
     def __getattr__(self, name):
         return getattr(self._core, name)
@@ -310,18 +315,13 @@ def build_field(self, t, coord=None, keep_edge=False):
         :param coord: If None, take the coordinate from the numerical solver.
         :return: None
         """
-
-        if None is coord:
-            _ = self.svr.ncoord
-            if keep_edge:
-                self.svr.xindices = np.linspace(
-                    0, (_ - 1), num=((_ + 1) // 2), dtype=int
-                )
-            else:
-                self.svr.xindices = np.linspace(
-                    2, (_ - 3), num=((_ - 3) // 2), dtype=int
-                )
-            # Use the numerical solver.
+        if coord is None:
+            _ = self.svr.ncoord - 1
+            start = 0 if keep_edge else 2
+            stop = _ if keep_edge else (_ - 2)
+            num = (stop - start) // 2 + 1
+            self.svr.xindices = np.linspace(start, stop, num, dtype='int32')
+            # set the x-coordinate for numerical solver.
             coord = self.svr.coord[self.svr.xindices]
         self.coord = coord.copy()  # Make a copy; no write back to argument.