is_empty for pseudo-matrices (#1691)

* Show method for pseudo-matrices modified

Added an output for pseudo-matrices with zero rows that

* Added an 'is_empty' method for pseudo-matrices

* Tests added for is_empty

* Added test for printing

src/NumFieldOrd/NfOrd/LinearAlgebra.jl

@@ -2052,3 +2052,12 @@ function inv(x::Generic.MatSpaceElem{AbsSimpleNumFieldOrderElem})
   K = nf(R)
   return change_base_ring(R, inv(change_base_ring(K, x)))
 end
+
+################################################################################
+#
+#  Emptiness check
+#
+################################################################################
+
+is_empty(P::PMat) = is_empty(matrix(P))
+

test/NfOrd/LinearAlgebra.jl

@@ -137,6 +137,31 @@
       @test Hecke._in_span(map(K, [1, 2, 3, 4]), A)[1]
       @test Hecke._in_span(map(K, [5, 6, 7, 8]), A)[1] == false
     end
+    @testset "emptiness" begin
+      K, a = quadratic_field(-5)
+      O = maximal_order(K)
+      ide = fractional_ideal(O, one(O))
+      pmat00 = pseudo_matrix(identity_matrix(K, 0), [])
+      pmat02 = pseudo_matrix(matrix(K, 0, 2, []), [])
+      pmat20 = pseudo_matrix(matrix(K, 2, 0, []), [ide, ide])
+      pmat11 = pseudo_matrix(identity_matrix(K, 1), [ide])
+      pmat23 = pseudo_matrix(matrix(K, 2, 3, [1, 2, 3, a, 2*a, 3*a]), [ide, ide])
+      @test is_empty(pmat00)
+      @test is_empty(pmat02)
+      @test is_empty(pmat20)
+      @test !is_empty(pmat11)
+      @test !is_empty(pmat23)
+      @test isempty(pmat00)
+      @test isempty(pmat02)
+      @test isempty(pmat20)
+      @test !is_empty(pmat11)
+      @test !is_empty(pmat23)
+
+      @test sprint(show, pmat00) isa String
+      @test sprint(show, pmat02) isa String
+      @test sprint(show, pmat20) isa String
+
+    end
   end
 
   @testset "rand" begin