Handle boundary and line-search fixed-effect inference

include/spectra_reml/fixed_effects.hpp

@@ -13,9 +13,11 @@ struct FixedEffectHypothesis {
     std::vector<double> rhs;
 };
 
-// Computes coefficient-wise tests and any supplied general linear hypotheses
-// at an already fitted REML solution.  Inputs must use the same (possibly GRM-
-// rotated) coordinate system and phenotype scale as the supplied fit.
+// Computes coefficient-wise tests and any supplied general linear hypotheses.
+// At an interior or retained line-search iterate it uses the requested REML
+// small-sample method.  A sigma_g2=0 boundary fit is refitted and tested as
+// ordinary least squares without a GRM term.  Inputs must use the same
+// orthogonally rotated coordinate system and phenotype scale as the fit.
 [[nodiscard]] FixedEffectInferenceResult infer_fixed_effects_spectral(
     const std::vector<double>& y_star, const ColMajorMatrix& x_star,
     const std::vector<double>& eigenvalues, const RemlResult& fit,

include/spectra_reml/types.hpp

@@ -66,6 +66,7 @@ enum class FitStatus {
 
 enum class FixedEffectTestMethod {
     none,
+    ordinary_least_squares,
     satterthwaite,
     kenward_roger
 };
@@ -75,7 +76,8 @@ enum class FixedEffectTestMethod {
 enum class FixedEffectInferenceStatus {
     not_requested,
     ok,
-    boundary_conditional,
+    boundary_ols,
+    line_search_conditional,
     fit_not_converged,
     invalid_contrast,
     information_singular,
@@ -99,8 +101,9 @@ struct FixedEffectInferenceResult {
     FixedEffectTestMethod method = FixedEffectTestMethod::none;
     FixedEffectInferenceStatus status =
         FixedEffectInferenceStatus::not_requested;
-    // One test per beta, in design-matrix column order.  Satterthwaite reports
-    // a signed t statistic; Kenward-Roger reports an F statistic with 1 NumDF.
+    // One test per beta, in design-matrix column order.  OLS and
+    // Satterthwaite report signed t statistics; Kenward-Roger reports an F
+    // statistic with 1 NumDF.
     std::vector<FixedEffectTestResult> coefficient_tests;
     // Optional general linear hypotheses requested by the caller.
     std::vector<FixedEffectTestResult> hypothesis_tests;