feat(demo): add new cells and relationships for enhanced calculations

Author: sean-parent

begin/src/app.rs

@@ -31,14 +31,26 @@ pub fn make_demo_sheet() -> (Sheet, Labels) {
         ])
         .unwrap();
 
+    let d = sheet.add_cell(4.0_f64);
+    let e = sheet.add_cell(5.0_f64);
+
+    let rel = sheet
+        .add_relationship(vec![
+            Method::from_fn_2_1([d, e], c, |x: &f64, y: &f64| Ok(x * y)),
+            Method::from_fn_2_1([c, e], d, |x: &f64, y: &f64| Ok(x / y)),
+            Method::from_fn_2_1([c, d], e, |x: &f64, y: &f64| Ok(x / y)),
+        ])
+        .unwrap();
+
     // Compute c = a × b = 6 on startup; clear changed so c does not pulse immediately.
     sheet.propagate().unwrap();
     sheet.clear_changed();
 
     labels.add_cell::<f64>(a, "a");
     labels.add_cell::<f64>(b, "b");
     labels.add_cell::<f64>(c, "c");
-    labels.add_relationship(rel, "×");
+    labels.add_cell::<f64>(d, "d");
+    labels.add_cell::<f64>(e, "e");
 
     (sheet, labels)
 }