avoid index type mismatch and unnecessary casting

include/evalhyd/detail/probabilist/ranks.hpp

@@ -57,7 +57,7 @@ namespace evalhyd
                 );
                 xt::view(max_ranks, xt::all()) = NAN;
                 
-                for (int m = 0; m < n_mbr; m++)
+                for (std::size_t m = 0; m < n_mbr; m++)
                 {
                     // strictly below a member and no rank yet
                     xt::view(ranks, xt::all()) = xt::where(
@@ -170,7 +170,7 @@ namespace evalhyd
                                 xt::view(r_k_masked, xt::all(), xt::all(),
                                          b_exp[e]);
 
-                        for (int j = 0; j < n_mbr + 1; j++)
+                        for (std::size_t j = 0; j < n_mbr + 1; j++)
                         {
                             // compute the observed relative frequency
                             // $o_j = \sum_{k \in M_j} r_k$