Error:does not contain a definition for '' and no extension method

hi,

I have a problem with my code , it is giving this error ('Net.Kniaz.AHP.AHPModel' does not contain a definition for 'AddCriteria' and no extension method 'AddCriteria' accepting a first argument of type 'Net.Kniaz.AHP.AHPModel' could be found (are you missing a using directive or an assembly reference?)) and I don't know what is the problem, I reviewed several similar question, but still couldn't find a solution. 

note: I'm a very beginner programmer :)

Here is my code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using DotNetMatrix;
using GeneralMatrix;
using NUnit.Framework;
using Net.Kniaz.AHP;

namespace Net.Kniaz.AHP
{
      public class AHPModel
     {
         public AHPModel(int n, int m);
     
         
         private GeneralMatrix _criteria;
         private GeneralMatrix _choiceMatrix;
         private GeneralMatrix _orderedCriteria;
         private GeneralMatrix _calculatedChoices;
         private int _ncriteria;
         private int _mchoice;
         private int _superDim;
      }
    public class TestAHP
    {
    public void TestVacationSpotSelection()
{
			double[][] criteria = new double[][]
								{ 
									new double[] {1,5,0.33333333,1},
									new double[] {0,1,0.2,0.5},
									new double[] {0,0,1,3},
									new double[] {0,0,0,1}
								};

			double[][] activitiesChoices = new double[][]
				{
					new double[] {1,4,3},
					new double[] {0,1,2},
					new double[] {0,0,1}
				};

			double[][] nightlifeChoices = new double[][]
				{
					new double[] {1,0.5,0.3333333},
					new double[] {0,1,0.5},
					new double[] {0,0,1}
				};

			double[][] siteseeingChoices = new double[][]
				{
					new double[] {1,0.142857,0.2},
					new double[] {0,1,2},
					new double[] {0,0,1}
				};

			double[][] costChoices = new double[][]
				{
					new double[] {1,3,5},
					new double[] {0,1,2},
					new double[] {0,0,1}
				};

			//4 criteria, 3 choices
       

			AHPModel model = new AHPModel(4,3);
			model.AddCriteria(criteria);
			model.AddCriterionRatedChoices(0,activitiesChoices);
			model.AddCriterionRatedChoices(1,nightlifeChoices);
			model.AddCriterionRatedChoices(2,siteseeingChoices);
			model.AddCriterionRatedChoices(3,costChoices);

			model.CalculateModel();

			GeneralMatrix calcCriteria = model.CalculatedCriteria;
			GeneralMatrix results = model.ModelResult;
			GeneralMatrix choices = model.CalculatedChoices;
			//choices: SF 42%, Orlando31%, NY 27%
			Assert.AreEqual(31,System.Math.Round(choices.GetElement(0,0)*100,0));
			Assert.AreEqual(42,System.Math.Round(choices.GetElement(1,0)*100,0));
			Assert.AreEqual(27,System.Math.Round(choices.GetElement(2,0)*100,0));


}
    }    
    }

the error is in the lines (5 to 13) lines from the end (model.)

thank you