Error CS0246: The type or namespace name `MLApp' could not be found. Are you missing an assembly reference?

I was trying to call Matlab function in C# scripts.

Here is the version of softwares I am using: Matlab: 8.6.0.267246 (R2015b) // Unity 2018.2.2.f1 // Visual Studio 15.7.6

To test the feasibility I set up a simple test code (shown below) added reference "MatlabApplication (Version 8.6) Type Library" and attached it to an empty object. However, I constantly met this compiler error when running this script in Unity.

I would really appreciate it if someone could give me some advice. I am familiar with Matlab but basically a novice in Unity and C# (just self-taught a week ago). Thank you in advance.

namespace MatlabExecution{ public class DanceWithMatlab : MonoBehaviour { public MLApp.MLApp matlab = new MLApp.MLApp();

     public DanceWithMatlab()
     {
         // Step 1:
         // Create the MATLAB instance 

         // Change to the directory where the function is located 
         matlab.Execute(@"cd C:xx"); // path name is omitted for privacy reason

         // Define the output 
         object result = null;

         // Call the MATLAB function 
         matlab.Feval("Test", 1, out result, 1, 2); // Matlab function name

         // Display result 
         object[] res = result as object[];
         Console.WriteLine(res[0]);
         //Debug.Log("The result is {0}", res[0]);

         matlab.Execute("quit");
     }
 }

}