Merge pull request #69 from IntegralEquations/zero-rkmatrix

Test aca on zero matrix

Author: maltezfaria

Project.toml

@@ -1,6 +1,6 @@
 name = "HMatrices"
 uuid = "8646bddf-ab1c-4fa7-9c51-ba187d647618"
-version = "0.2.8"
+version = "0.2.9"
 
 [deps]
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"

src/compressor.jl

@@ -134,6 +134,14 @@ function _aca_partial(K, irange, jrange, atol, rmax, rtol, istart, buffer_ = not
         if svdvals(δ)[end] == 0
             @debug "zero pivot found during partial aca"
             i = findfirst(x -> x == true, I)
+            if isnothing(i)
+                # ran out of candidate rows. Good case: the matrix is zero. Bad
+                # case: aca failed
+                all(j -> iszero(K[first(irange), j]), jrange) &&
+                    all(i -> iszero(K[i, first(jrange)]), irange) ||
+                    @warn "aca possibly failed on $irange × $jrange"
+                break
+            end
         else # δ != 0
             iδ = inv(δ)
             # rdiv!(b,δ) # b <-- b/δ

test/compressor_test.jl

@@ -31,6 +31,10 @@ Random.seed!(1)
         R = aca(M, irange, jrange)
         @test rank(R) == r
 
+        # test zero matrix
+        R = aca(zero(M), irange, jrange)
+        @test norm(Matrix(R)) ≈ 0.0
+
         # test fast update of frobenius norm
         m, n = 10000, 1000
         r = 10