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Set out invariants for column indices

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This should make it safe to use the elements' column indices outside the
realization method—for unpacking tangent vectors, at least.
This commit is contained in:
Aaron Fenyes 2024-12-18 09:49:14 -08:00
parent 967daa595d
commit e2c5ba0fc7
1 changed files with 21 additions and 6 deletions
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27
app-proto/src/assembly.rs
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@ -134,7 +134,16 @@ pub struct Assembly {
pub elements: Signal<Slab<Element>>, pub elements: Signal<Slab<Element>>,
pub constraints: Signal<Slab<Constraint>>, pub constraints: Signal<Slab<Constraint>>,
// solution variety tangent space // solution variety tangent space. the basis vectors are stored in
// configuration matrix format, ordered according to the elements' column
// indices. when you realize the assembly, every element that's present
// during realization gets a column index and is reflected in the tangent
// space. since the methods in this module never assign column indices
// without later realizing the assembly, we get the following invariant:
//
// (1) if an element has a column index, its tangent motions can be found
// in that column of the tangent space basis matrices
//
pub tangent: Signal<ConfigSubspace>, pub tangent: Signal<ConfigSubspace>,
// indexing // indexing
@ -291,6 +300,14 @@ impl Assembly {
// --- deformation --- // --- deformation ---
// project the given motion to the tangent space of the solution variety and
// move the assembly along it. the implementation is based on invariant (1)
// from above and the following additional invariant:
//
// (2) if an element is affected by a constraint, it has a column index
//
// we have this invariant because the assembly gets realized each time you
// add a constraint
pub fn deform(&self, motion: AssemblyMotion) { pub fn deform(&self, motion: AssemblyMotion) {
/* KLUDGE */ /* KLUDGE */
// when the tangent space is zero, deformation won't do anything, but // when the tangent space is zero, deformation won't do anything, but
@ -319,11 +336,9 @@ impl Assembly {
None => { None => {
// give the element a column index, even though it's never // give the element a column index, even though it's never
// been through a realization, and add its motion to that // been through a realization, and add its motion to that
// column of the projected motion. this puts the element // column of the projected motion. this temporarily breaks
// column indices out of sync with the saved tangent space, // invariant (1), but the invariant will be restored when we
// but that's okay: the realization we do to get back onto // realize the assembly at the end of the deformation
// the solution variety will re-index the elements and
// recompute the tangent space
let mut target_column = motion_proj.column_mut(next_column_index); let mut target_column = motion_proj.column_mut(next_column_index);
target_column += elt_motion.velocity; target_column += elt_motion.velocity;
self.elements.update_silent( self.elements.update_silent(