Fix test for repeated wave vectors in SampledCorrelations

docs/src/versions.md

@@ -1,5 +1,11 @@
 # Version History
 
+## v0.7.2
+(In development)
+
+* Fix error in `SampledCorrelations` with a coarse ``𝐪``-grid. ([PR
+  #314](https://github.com/SunnySuite/Sunny.jl/pull/314))
+
 ## v0.7.1
 (Sep 3, 2024)
 

src/SampledCorrelations/DataRetrieval.jl

@@ -14,8 +14,10 @@ function pruned_wave_vector_info(sc::SampledCorrelations, qs)
     # Convert to absolute units (for form factors)
     qabs_rounded = map(m -> sc.crystal.recipvecs * (m ./ sc.sys_dims), ms)
 
-    # List of "starting" pointers i where idcs[i-1] != idcs[i]
-    starts = findall(i -> i == 1 || idcs[i-1] != idcs[i], eachindex(idcs))
+    # List of "starting" pointers i where qabs_rounded[i-1] != qabs_rounded[i],
+    # i.e., indices where the desired wave vector is distinct from the previous
+    # one.
+    starts = findall(i -> i == 1 || !isapprox(qabs_rounded[i-1], qabs_rounded[i]), eachindex(qabs_rounded))
 
     # Length of each run of repeated values
     counts = starts[2:end] - starts[1:end-1]

test/test_correlation_sampling.jl

@@ -93,6 +93,13 @@
     true_static_vals = intensities_static(res, qgrid)
     true_static_total = sum(true_static_vals.data)
     @test isapprox(true_static_total / prod(sys.dims), 1.0; atol=1e-12)
+
+    # Test whether two distinct wave vectors referencing the same underlying
+    # data point in sc.data are in fact treated differently.
+    formfactors = [1 => FormFactor("Fe2")]
+    sc.measure = ssf_trace(sys; apply_g=false, formfactors)
+    res = intensities_static(sc, [[0, 0, 1/2], [1, 0, 1/2]]; kT=nothing)
+    @test res.data[1] != res.data[2]
 end
 
 @testitem "Merge correlations" begin