Load an LP and modify it by adding an extra constraint

               Maximize
                   2x + y
               subject to
                   c1:  x + 4y <= 24
                   c2:       y <=  5
                   c3: 3x +  y <= 20
                   c4:  x +  y <=  9
               and
                   0 <= x,y <= +infinity

               c5: 6x + y <= 20

using System;
using Optimizer;

namespace XPRSExamples
{
	class LoadLP
	{
		public static void Main(string[] args)
		{
			LoadLP example = new LoadLP();
			example.Run();
		}

		private void Run()
		{
			
			// Store the problem
			// Row data
			int nRow = 4;
			char[] sRowType = {'L', 'L', 'L', 'L'};
			double[] dRHS = { 24.0, 5.0, 20.0, 9.0 };
			string[] sRowName = { "c1", "c2", "c3", "c4"  };

			// Column data
			int nCol = 2;
			double[] dObj = { 2.0, 1.0 };      
			double[] dLowerBd = { 0,0};
			double[] dUpperBd = { XPRS.PLUSINFINITY, XPRS.PLUSINFINITY };

			string[] sColName = { "x", "y" };
			      
			// Matrix data
			int[] nColStart = { 0,3,7 };
			int[] nRowInd = {0,2,3,0,1,2,3 };
			double[] dMatElem = { 1,3,1,4,1,1,1 };

			// Store extra constraint
			int nNewRow = 1;
			int nNewElem = 2;
			char[] sNewRowType = {'L'};
			string[] sNewRowName = {"c5"};

			double[] dNewRHS = {20};
			double[] dNewRowElem = { 6,1 };
			int[] nNewRowStart = { 0,2 };
			int[] nNewColInd = { 0,1 };

			double dObjValue;


			string sLogFile = "loadlp.log";
			string sProblem1 = "lp";
			string sProblem2 = "revised";

			try
			{
				XPRS.Init("");
				
				prob = new XPRSprob();
				prob.SetLogFile(sLogFile);
				
				// Tell Optimizer to call OptimizerMsg whenever a message is output
				prob.MessageCallbacks += new MessageCallback (this.OptimizerMsg);
				
				prob.LoadLP(sProblem1, nCol, nRow, sRowType, dRHS, null, dObj, nColStart, null, nRowInd, dMatElem, dLowerBd, dUpperBd);
                prob.ChgObjSense(ObjSense.Maximize); 

				// Add row names
				prob.AddNames(1, sRowName, 0, nRow -1 );

				// Add column names
				prob.AddNames(2, sColName, 0, nCol -1 );

				// Output the matrix
				prob.WriteProb(sProblem1, "");

				// Solve the LP problem
				prob.LpOptimize();
				
				// Get and display the value of the objective function
				dObjValue = prob.LPObjVal;
				Console.WriteLine("The optimal objective value is {0}", dObjValue);

				// ** Add the extra constraint and solve again **

				// Add new row
				prob.AddRows(nNewRow, nNewElem, sNewRowType, dNewRHS, null, nNewRowStart, nNewColInd, dNewRowElem);
				   
				// Add new row name
				prob.AddNames(1, sNewRowName, nRow, nRow);
				   
				// Output the revised matrix
				prob.WriteProb(sProblem2, "");
				Console.WriteLine("Matrix file {0}.mat has been created", sProblem2);

				// Solve with dual - since the revised problem inherits dual feasibility
				// from the original
				prob.LpOptimize("d");
				   
				// Get and display the value of the objective function
				dObjValue = prob.LPObjVal;
				Console.WriteLine("The revised optimal objective value is {0}",dObjValue);

			}

			catch (XPRSException e)
			{
				Console.WriteLine(e.ToString());
        throw e;
			}
			finally
			{
				prob.Destroy();
				XPRS.Free();
			}
		}

		public void OptimizerMsg (XPRSprob prob, object data, string message, int len, int msglvl)
		{
			switch(msglvl)
			{
				case 3:
				case 4:
					Console.WriteLine ("{0}" + message, data);
					break;
			}
		}

		private XPRSprob prob;
	}
}

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>

    <IsPackable>false</IsPackable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="FICO.Xpress.XPRSdn" Version="38.1.2" /> <!-- Version 38.01.02 or later -->
  </ItemGroup>
  

</Project>