Helmholtz testing (no decay bug)

Core/GhostBuffer.cs

@@ -0,0 +1,27 @@
+namespace FluidSim.Core
+{
+    public class GhostBuffer
+    {
+        public float[] Rho, U, P, Y;
+        public int PipeCount { get; }
+
+        public GhostBuffer(int pipeCount)
+        {
+            PipeCount = pipeCount;
+            int size = pipeCount * 2;
+            Rho = new float[size];
+            U = new float[size];
+            P = new float[size];
+            Y = new float[size];
+        }
+
+        public void Set(int pipeIndex, bool isLeftEnd, float rho, float u, float p, float y)
+        {
+            int idx = pipeIndex * 2 + (isLeftEnd ? 0 : 1);
+            Rho[idx] = rho;
+            U[idx] = u;
+            P[idx] = p;
+            Y[idx] = y;
+        }
+    }
+}