From dc067976eb4efbf9fd5dbc663bd97850c2a30121 Mon Sep 17 00:00:00 2001
From: Aaron Fenyes <aaron.fenyes@fareycircles.ooo>
Date: Wed, 18 Dec 2024 00:25:15 -0800
Subject: [PATCH] Implement projection onto the zero subspace

---
 app-proto/src/engine.rs | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/app-proto/src/engine.rs b/app-proto/src/engine.rs
index 36998bd..e96ea52 100644
--- a/app-proto/src/engine.rs
+++ b/app-proto/src/engine.rs
@@ -141,13 +141,15 @@ impl ConfigSubspace {
     
     // find the projection onto this subspace of the motion where the element
     // with the given column index has velocity `v`
-    /* TO DO */
-    // for the zero subspace, this method's behavior doesn't match its name: it
-    // panics rather than returning zero
     pub fn proj(&self, v: &DVectorView<f64>, column_index: usize) -> DMatrix<f64> {
-        self.basis.iter().map(
-            |b| b.column(column_index).dot(&v) * b
-        ).sum()
+        if self.dim() == 0 {
+            const ELEMENT_DIM: usize = 5;
+            DMatrix::zeros(ELEMENT_DIM, self.assembly_dim)
+        } else {
+            self.basis.iter().map(
+                |b| b.column(column_index).dot(&v) * b
+            ).sum()
+        }
     }
 }