C#

double[][] d = new double[2][];
for (int i = 0; i < 2; i++)
{
   d[i] = new double[2];
   for (int j = 0; j < 2; j++)
      d[i][j] = i + j;
}	
XmlSerializer xs = new XmlSerializer(typeof(double[][]));
xs.Serialize(Console.Out, d);

double[][] d = new double[2][];
for(int i = 0; i < d.Length; i++)
{
	d[i] = new double[2];
}

BinaryFormatter b = new BinaryFormatter();
using(FileStream fs = new FileStream("test.bin", FileMode.Create))
{
	b.Serialize(fs, d);
}

[Serializable]
public class DoubleArray
{
   double[,] data;
   [XmlArray(typeof(double[,])]
   public double[,] Data
   { 
            get{}
            set{}
   }
}

public class UseStuff
{
   DoubleArray array = new DoubleArray();
   ... // do your stuff ...
   
   XmlSerializer ser = new XmlSerializer(typeof(DoubleArray));
   using ( FileStream stream = File.Create(path) )
   {
            ser.Serialize(stream, array);
   }
}

public PrimaryData GetPrimaryList(string key)
{
     return GetPrimaryDataObjects(key, connection);
}

public SecondaryList GetSecondaryList(string key)
{
     return GetSecondaryDataObjects(key, connection);
}