Fixing bug in static_assert for bounds checking

matrix.hpp

@@ -154,11 +154,11 @@ typename std::enable_if<!is_matrix<_type>::value, matrix<t, r, c> >::type
       return { _data[row] };
     }
     row_reference<const T, C> at(std::size_t row) const {
-      expects(row >= R, std::out_of_range, "row index out of range");
+      expects(row < R, std::out_of_range, "row index out of range");
       return operator[](row);
     }
     row_reference<T, C> at(std::size_t row) {
-      expects(row >= R, std::out_of_range, "row index out of range");
+      expects(row < R, std::out_of_range, "row index out of range");
       return operator[](row);
     }
     value_type const & at(std::size_t row, std::size_t col) const {