Explain why the empty-assembly case is special

In the process, switch from the `web-sys` crate's `console::log_1`
function to Sycamore's more flexible `console_log` macro. The latter
works both inside and outside the browser, so we can use it without
checking whether we're compiling to WebAssembly.

app-proto/src/assembly.rs

@@ -16,7 +16,6 @@ use crate::{
     components::{display::DisplayItem, outline::OutlineItem},
     engine::{
         Q,
-        change_half_curvature,
         local_unif_to_std,
         point,
         project_point_to_normalized,
@@ -358,16 +357,6 @@ pub trait Regulator: Serial + ProblemPoser + OutlineItem {
     fn subjects(&self) -> Vec<Rc<dyn Element>>;
     fn measurement(&self) -> ReadSignal<f64>;
     fn set_point(&self) -> Signal<SpecifiedValue>;
-    
-    // this method is used to responsively precondition the assembly for
-    // realization when the regulator becomes a constraint, or is edited while
-    // acting as a constraint. it should track the set point, do any desired
-    // preconditioning when the set point is present, and use its return value
-    // to report whether the set is present. the default implementation does no
-    // preconditioning
-    fn try_activate(&self) -> bool {
-        self.set_point().with(|set_pt| set_pt.is_present())
-    }
 }
 
 impl Hash for dyn Regulator {
@@ -488,18 +477,6 @@ impl Regulator for HalfCurvatureRegulator {
     fn set_point(&self) -> Signal<SpecifiedValue> {
         self.set_point
     }
-    
-    fn try_activate(&self) -> bool {
-        match self.set_point.with(|set_pt| set_pt.value) {
-            Some(half_curv) => {
-                self.subject.representation().update(
-                    |rep| change_half_curvature(rep, half_curv)
-                );
-                true
-            }
-            None => false
-        }
-    }
 }
 
 impl Serial for HalfCurvatureRegulator {
@@ -552,8 +529,7 @@ pub struct Assembly {
     pub elements_by_id: Signal<BTreeMap<String, Rc<dyn Element>>>,
     
     // realization control
-    pub keep_realized: Signal<bool>,
+    pub realization_trigger: Signal<()>,
-    pub needs_realization: Signal<bool>,
     
     // realization diagnostics
     pub realization_status: Signal<Result<(), String>>,
@@ -568,21 +544,23 @@ impl Assembly {
             regulators: create_signal(BTreeSet::new()),
             tangent: create_signal(ConfigSubspace::zero(0)),
             elements_by_id: create_signal(BTreeMap::default()),
-            keep_realized: create_signal(true),
+            realization_trigger: create_signal(()),
-            needs_realization: create_signal(false),
             realization_status: create_signal(Ok(())),
             descent_history: create_signal(DescentHistory::new())
         };
         
-        // realize the assembly whenever it becomes simultaneously true that
+        // realize the assembly whenever the element list, the regulator list,
-        // we're trying to keep it realized and it needs realization
+        // a regulator's set point, or the realization trigger is updated
         let assembly_for_effect = assembly.clone();
         create_effect(move || {
-            let should_realize = assembly_for_effect.keep_realized.get()
+            assembly_for_effect.elements.track();
-                && assembly_for_effect.needs_realization.get();
+            assembly_for_effect.regulators.with(
-            if should_realize {
+                |regs| for reg in regs {
-                assembly_for_effect.realize();
+                    reg.set_point().track();
-            }
+                }
+            );
+            assembly_for_effect.realization_trigger.track();
+            assembly_for_effect.realize();
         });
         
         assembly
@@ -646,19 +624,6 @@ impl Assembly {
             regulators.update(|regs| regs.insert(regulator.clone()));
         }
         
-        // request a realization when the regulator becomes a constraint, or is
-        // edited while acting as a constraint
-        let self_for_effect = self.clone();
-        create_effect(move || {
-            /* DEBUG */
-            // log the regulator update
-            console_log!("Updated regulator with subjects {:?}", regulator.subjects());
-            
-            if regulator.try_activate() {
-                self_for_effect.needs_realization.set(true);
-            }
-        });
-        
         /* DEBUG */
         // print an updated list of regulators
         console_log!("Regulators:");
@@ -726,8 +691,10 @@ impl Assembly {
         } else {
             console_log!("✅️ Target accuracy achieved!");
         }
-        console_log!("Steps: {}", history.scaled_loss.len() - 1);
+        if history.scaled_loss.len() > 0 {
-        console_log!("Loss: {}", history.scaled_loss.last().unwrap());
+            console_log!("Steps: {}", history.scaled_loss.len() - 1);
+            console_log!("Loss: {}", history.scaled_loss.last().unwrap());
+        }
         
         // report the loss history
         self.descent_history.set(history);
@@ -750,9 +717,6 @@ impl Assembly {
                 
                 // save the tangent space
                 self.tangent.set_silent(tangent);
-                
-                // clear the realization request flag
-                self.needs_realization.set(false);
             },
             Err(message) => {
                 // report the realization status. the `Err(message)` we're
@@ -848,10 +812,10 @@ impl Assembly {
             });
         }
         
-        // request a realization to bring the configuration back onto the
+        // trigger a realization to bring the configuration back onto the
         // solution variety. this also gets the elements' column indices and the
         // saved tangent space back in sync
-        self.needs_realization.set(true);
+        self.realization_trigger.set(());
     }
 }
 

app-proto/src/components/add_remove.rs

@@ -14,7 +14,22 @@ pub fn AddRemove() -> View {
             button(
                 on:click=|_| {
                     let state = use_context::<AppState>();
-                    state.assembly.insert_element_default::<Sphere>();
+                    batch(|| {
+                        // this call is batched to avoid redundant realizations.
+                        // it updates the element list and the regulator list,
+                        // which are both tracked by the realization effect
+                        /* TO DO */
+                        // it would make more to do the batching inside
+                        // `insert_element_default`, but that will have to wait
+                        // until Sycamore handles nested batches correctly.
+                        //
+                        //   https://github.com/sycamore-rs/sycamore/issues/802
+                        //
+                        // the nested batch issue is relevant here because the
+                        // assembly loaders in the test assembly chooser use
+                        // `insert_element_default` within larger batches
+                        state.assembly.insert_element_default::<Sphere>();
+                    });
                 }
             ) { "Add sphere" }
             button(

app-proto/src/components/test_assembly_chooser.rs

@@ -900,9 +900,6 @@ pub fn TestAssemblyChooser() -> View {
             let state = use_context::<AppState>();
             let assembly = &state.assembly;
             
-            // pause realization
-            assembly.keep_realized.set(false);
-            
             // clear state
             assembly.regulators.update(|regs| regs.clear());
             assembly.elements.update(|elts| elts.clear());
@@ -923,9 +920,6 @@ pub fn TestAssemblyChooser() -> View {
                 "irisawa-hexlet" => load_irisawa_hexlet_assemb(assembly),
                 _ => ()
             };
-            
-            // resume realization
-            assembly.keep_realized.set(true);
         });
     });
     

app-proto/src/engine.rs

@@ -1,7 +1,6 @@
 use lazy_static::lazy_static;
 use nalgebra::{Const, DMatrix, DVector, DVectorView, Dyn, SymmetricEigen};
 use std::fmt::{Display, Error, Formatter};
-use web_sys::{console, wasm_bindgen::JsValue}; /* DEBUG */
 
 // --- elements ---
 
@@ -50,40 +49,6 @@ pub fn project_point_to_normalized(rep: &mut DVector<f64>) {
     rep.scale_mut(0.5 / rep[3]);
 }
 
-// given a sphere's representation vector, change the sphere's half-curvature to
-// `half-curv` and then restore normalization by contracting the representation
-// vector toward the curvature axis
-pub fn change_half_curvature(rep: &mut DVector<f64>, half_curv: f64) {
-    // set the sphere's half-curvature to the desired value
-    rep[3] = half_curv;
-    
-    // restore normalization by contracting toward the curvature axis
-    const SIZE_THRESHOLD: f64 = 1e-9;
-    let half_q_lt = -2.0 * half_curv * rep[4];
-    let half_q_lt_sq = half_q_lt * half_q_lt;
-    let mut spatial = rep.fixed_rows_mut::<3>(0);
-    let q_sp = spatial.norm_squared();
-    if q_sp < SIZE_THRESHOLD && half_q_lt_sq < SIZE_THRESHOLD {
-        spatial.copy_from_slice(
-            &[0.0, 0.0, (1.0 - 2.0 * half_q_lt).sqrt()]
-        );
-    } else {
-        let scaling = half_q_lt + (q_sp + half_q_lt_sq).sqrt();
-        spatial.scale_mut(1.0 / scaling);
-        rep[4] /= scaling;
-    }
-    
-    /* DEBUG */
-    // verify normalization
-    let rep_for_debug = rep.clone();
-    console::log_1(&JsValue::from(
-        format!(
-            "Sphere self-product after curvature change: {}",
-            rep_for_debug.dot(&(&*Q * &rep_for_debug))
-        )
-    ));
-}
-
 // --- partial matrices ---
 
 pub struct MatrixEntry {
@@ -199,13 +164,6 @@ impl ConfigSubspace {
             ).collect::<Vec<_>>().as_slice()
         );
         
-        /* DEBUG */
-        // print the eigenvalues
-        #[cfg(all(target_family = "wasm", target_os = "unknown"))]
-        console::log_1(&JsValue::from(
-            format!("Eigenvalues used to find kernel:{}", eig.eigenvalues)
-        ));
-        
         // express the basis in the standard coordinates
         let basis_std = proj_to_std * &basis_proj;
         
@@ -425,9 +383,22 @@ pub fn realize_gram(
     // start the descent history
     let mut history = DescentHistory::new();
     
+    // handle the case where the assembly is empty. our general realization
+    // routine can't handle this case because it builds the Hessian using
+    // `DMatrix::from_columns`, which panics when the list of columns is empty
+    let assembly_dim = guess.ncols();
+    if assembly_dim == 0 {
+        let result = Ok(
+            ConfigNeighborhood {
+                config: guess.clone(),
+                nbhd: ConfigSubspace::zero(0)
+            }
+        );
+        return Realization { result, history }
+    }
+    
     // find the dimension of the search space
     let element_dim = guess.nrows();
-    let assembly_dim = guess.ncols();
     let total_dim = element_dim * assembly_dim;
     
     // scale the tolerance