Add example using evalexpr

multigrid/examples/expressions_vortex.json

@@ -0,0 +1,29 @@
+{
+    "grids": {
+        "grid": {
+            "x": { "linspace": { "start": -5, "end": 5, "steps": 100 } },
+            "y": { "linspace": { "start": -5, "end": 5, "steps": 100 } },
+            "boundary_conditions": {
+                "south": "this",
+                "north": "this",
+                "east": "this",
+                "west": "this"
+            },
+            "operators": {
+                "xi": "upwind9",
+                "eta": "upwind9"
+            }
+        }
+    },
+
+    "initial_conditions": {
+        "expressions": {
+            "globals": "uinf=1;vinf=0;beta=5;y0=0;x0=0;Tfactor=(GAMMA-1)*beta*beta/(8*GAMMA*PI*PI)",
+            "rho": "math::pow(1 - Tfactor*math::exp(1 - ((x-x0)*(x-x0) + (y-y0)*(y-y0))), 1.0/(GAMMA - 1))",
+            "u": "uinf + beta/(2*PI) * math::exp((1 - ((x-x0)*(x-x0) + (y-y0)*(y-y0)))/2)*(-(y-y0))",
+            "v": "vinf + beta/(2*PI) * math::exp((1 - ((x-x0)*(x-x0) + (y-y0)*(y-y0)))/2)*((x-x0))",
+            "p": "math::pow(rho, GAMMA)"
+        }
+    },
+    "integration_time": 2.0
+}