diff --git a/multigrid/src/main.rs b/multigrid/src/main.rs
index ae3e6b0..12fa9db 100644
--- a/multigrid/src/main.rs
+++ b/multigrid/src/main.rs
@@ -293,7 +293,7 @@ fn main() {
     } = config.into_runtime();
 
     let mut sys = System::new(grids, grid_connections, operators);
-    match initial_conditions {
+    match &initial_conditions {
         /*
         parsing::InitialConditions::File(f) => {
             for grid in &sys.grids {
@@ -371,23 +371,26 @@ fn main() {
     }
 
     output.add_timestep(ntime, &sys.fnow);
-    /*
+
     if opt.error {
         let time = ntime as Float * dt;
         let mut e = 0.0;
         for ((fmod, grid), op) in sys.fnow.iter().zip(&sys.grids).zip(&sys.operators) {
             let mut fvort = fmod.clone();
-            fvort.vortex(
-                grid.x(),
-                grid.y(),
-                time,
-                &vortexparams.as_ref().unwrap().clone(),
-            );
+            match &initial_conditions {
+                parsing::InitialConditions::Vortex(vortexparams) => {
+                    fvort.vortex(grid.x(), grid.y(), time, &vortexparams);
+                }
+                parsing::InitialConditions::Expressions(expr) => {
+                    let (rho, rhou, rhov, e) = fvort.components_mut();
+                    expr.as_ref()
+                        .evaluate(time, grid.x(), grid.y(), rho, rhou, rhov, e)
+                }
+            }
             e += fmod.h2_err(&fvort, &**op);
         }
         outinfo.error = Some(e);
     }
-    */
 
     if opt.output_json {
         println!("{}", json5::to_string(&outinfo).unwrap());