add 'tools::make_vector' to make it easier to optimize functions with a 1D output

src/limbo/tools/random_generator.hpp

@@ -53,6 +53,16 @@ namespace limbo {
             return ((Eigen::VectorXd::Random(size)).array() + 1.0) / 2.0;
         }
 
+        /// @ingroup tools
+        /// make a 1-D vector from a double (useful when we need to return vectors)
+        Eigen::VectorXd make_vector(double x)
+        {
+          Eigen::VectorXd res(1);
+          res(0) = x;
+          return res;
+        }
+
+
         /// @ingroup tools
         /// a mt19937-based random generator (mutex-protected)
         ///
@@ -84,7 +94,7 @@ namespace limbo {
         /// @ingroup tools
         /// Double random number generator
         using rgen_double_t = RandomGenerator<rdist_double_t>;
-        
+
         ///@ingroup tools
         ///integer random number generator
         using rgen_int_t = RandomGenerator<rdist_int_t>;