Added public enum HessianFormat, public class HighsHessian and privat…

…e static extern int Highs_passHessian to highs_csharp_api.cs

src/interfaces/highs_csharp_api.cs

@@ -19,6 +19,12 @@ public enum HighsMatrixFormat
     kRowwise
 }
 
+public enum HessianFormat
+{
+    kTriangular = 1,
+    kSquare
+}
+
 public enum HighsBasisStatus
 {
     kLower = 0,
@@ -104,6 +110,27 @@ public HighsModel(double[] colcost, double[] collower, double[] colupper, double
     }
 }
 
+public class HighsHessian
+{
+    public HessianFormat q_format;
+    public int[] qstart;
+    public int[] qindex;
+    public double[] qvalue;
+
+    public HighsHessian()
+    {
+
+    }
+
+    public HighsHessian(int[] qstart, int[] qindex, double[] qvalue, HessianFormat q_format = HessianFormat.kTriangular)
+    {
+        this.qstart = qstart;
+        this.qindex = qindex;
+        this.qvalue = qvalue;
+        this.q_format = q_format;
+    }
+}
+
 public class HighsSolution
 {
     public double[] colvalue;
@@ -236,6 +263,16 @@ private static extern int Highs_passMip(
         double[] avalue,
         int[] highs_integrality);
 
+    [DllImport(highslibname)]
+    private static extern int Highs_passHessian(
+        IntPtr highs,
+        int dim,
+        int numnz,
+        int q_format,
+        int[] qstart,
+        int[] qindex,
+        double[] qvalue);
+
     [DllImport(highslibname)]
     private static extern int Highs_setOptionValue(IntPtr highs, string option, string value);