--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ext/DiffinitiveSparseArraysExt.jl	Sun Oct 20 21:38:09 2024 +0200
@@ -0,0 +1,25 @@
+module DiffinitiveSparseArraysExt
+
+using Diffinitive
+using Diffinitive.LazyTensors
+
+using SparseArrays
+using Tokens
+
+"""
+    sparse(t::LazyTensor)
+
+The sparse matrix representation of `t`.
+
+If `L` is a `LazyTensor` and `v` a tensor, then `A = sparse(L)` is constructed
+so that `A*reshape(v,:) == reshape(L*v,:)`.
+"""
+function SparseArrays.sparse(t::LazyTensor)
+    v = ArrayToken(:v, prod(domain_size(t)))
+
+    v̄ = reshape(v,domain_size(t)...)
+    tv = reshape(t*v̄, :)
+    return Tokens._to_matrix(tv, prod(range_size(t)), prod(domain_size(t)))
+end
+
+end