more algorithm traits

Author: lkdvos

src/algorithms.jl

@@ -95,6 +95,54 @@ right_orth_kind(alg::AbstractAlgorithm) = error(
     """
 )
 
+"""
+    left_null_kind(alg::AbstractAlgorithm) -> f!
+
+Select an appropriate factorization function for applying `left_null!(A, alg)`.
+By default, this is either `left_null_qr!` or `left_null_svd!`, but this can be extended
+to insert arbitrary other decomposition functions, which should follow the signature
+`f!(A, F, alg) -> F`
+"""
+function left_null_kind(alg::AbstractAlgorithm)
+    left_orth_kind(alg) === left_orth_qr! && return left_null_qr!
+    left_orth_kind(alg) === left_orth_svd! && return left_null_svd!
+    return error(
+        """
+        Unkown or invalid `left_null` algorithm type `$(typeof(alg))`.
+        To register the algorithm type, define:
+
+                MatrixAlgebraKit.left_null_kind(alg) = f!
+
+        where `f!` should be the factorization function that will be used.
+        By default, this is either `left_null_qr!` or `left_null_svd!`.
+        """
+    )
+end
+
+"""
+    right_null_kind(alg::AbstractAlgorithm) -> f!
+
+Select an appropriate factorization function for applying `right_null!(A, alg)`.
+By default, this is either `right_null_lq!` or `right_null_svd!`, but this can be extended
+to insert arbitrary other decomposition functions, which should follow the signature
+`f!(A, F, alg) -> F`
+"""
+function right_null_kind(alg::AbstractAlgorithm)
+    right_orth_kind(alg) === right_orth_lq! && return right_null_lq!
+    right_orth_kind(alg) === right_orth_svd! && return right_null_svd!
+    return error(
+        """
+        Unkown or invalid `right_null` algorithm type `$(typeof(alg))`.
+        To register the algorithm type, define:
+
+                MatrixAlgebraKit.right_null_kind(alg) = f!
+
+        where `f!` should be the factorization function that will be used.
+        By default, this is either `right_null_lq!` or `right_null_svd!`.
+        """
+    )
+end
+
 """
     does_truncate(alg::AbstractAlgorithm) -> Bool