Fix overflow and type issues with generic det of a triangular matrix (#1418)

Fixes #1415

---------

Co-authored-by: Steven G. Johnson <[email protected]>

Author: 2 people

src/generic.jl

@@ -1821,7 +1821,7 @@ julia> det(BigInt[1 0; 2 2]) # exact integer determinant
 function det(A::AbstractMatrix{T}) where {T}
     if istriu(A) || istril(A)
         S = promote_type(T, typeof((one(T)*zero(T) + zero(T))/one(T)))
-        return convert(S, det(UpperTriangular(A)))
+        return prod(Base.Fix1(convert, S), @view A[diagind(A)]; init=one(S))
     end
     return det(lu(A; check = false))
 end

test/generic.jl

@@ -25,6 +25,9 @@ using .Main.FillArrays
 isdefined(Main, :SizedArrays) || @eval Main include(joinpath($(BASE_TEST_PATH), "testhelpers", "SizedArrays.jl"))
 using .Main.SizedArrays
 
+isdefined(Main, :Furlongs) || @eval Main include(joinpath($(BASE_TEST_PATH), "testhelpers", "Furlongs.jl"))
+using .Main.Furlongs
+
 Random.seed!(123)
 
 n = 5 # should be odd
@@ -103,6 +106,18 @@ n = 5 # should be odd
     @testset "det with nonstandard Number type" begin
         elty <: Real && @test det(Dual.(triu(A), zero(A))) isa Dual
     end
+    if elty <: Int
+        @testset "det no overflow - triangular" begin
+            A = diagm([typemax(elty), typemax(elty)])
+            @test det(A) == det(float(A))
+        end
+    end
+    @testset "det with units - triangular" begin
+        for dim in 0:4
+            A = diagm(Furlong.(ones(elty, dim)))
+            @test det(A) == Furlong{dim}(one(elty))
+        end
+    end
 end
 
 @testset "diag" begin