fix issue reported by Ali for primitive of Fourier lattice (conversio…

…n to integer issue)

src/lattices.jl

@@ -226,7 +226,12 @@ function transform(flat::AbstractFourierLattice{D}, P::AbstractMatrix{<:Real}) w
     # transform all k-vecs in the orbits
     for (i, orb) in enumerate(orbits)
         for (j, k) in enumerate(orb)
-            orbits′[i][j] = convert(SVector{D, Int}, P'*k)
+            k′ = P'*k
+            int_k′ = round.(Int, k′)
+            if !isapprox(k′, k, atol=DEFAULT_ATOL)
+                error("unexpectedly obtained non-integer k-vector in orbit")
+            end
+            orbits′[i][j] = int_k′::SVector{D,Int}
         end
     end
     # --- Comment regarding the `convert(SVector{D, Int}, ...)` call above: ---

test/lattices.jl

@@ -12,4 +12,8 @@ using Test
         # test that a primitivize -> conventionalize cycle leaves the lattice unchanged
         @test flat ≈ conventionalize(flat′, cntr)
     end
+
+    # convert-to-integer bug found by Ali
+    flat = levelsetlattice(sgnum, Val(3), ntuple(_->2, Val(3)))
+    @test primitivize(flat, centering(sgnum)) isa UnityFourierLattice{3} # = doesn't throw
 end