Sum of dictionary value

 Dictionary<string, int[,]> Matrices = new Dictionary<string, int[,]
//Get the values of dictionary in an array
 public object[] Tab_Mat(Dictionary<string, int[,]> a)
        {
            object[] ruleArray = new object[a.Count];
            int num = 0;
            foreach (KeyValuePair<string, int[,]> rule in a)
                ruleArray[num++] = rule.Value;
            return ruleArray;
        }
//Get the sum of the values of the dictionary
public int[,] sum_global_Mat(Dictionary<string, int[,]> config)
        {
            var a = Tab_Mat(config);
            var newArray = Array.ConvertAll(a, item => (int[,])item);
            int[,] m = new int[newArray[0].GetLength(0), newArray[0].GetLength(1)];
            for ( int i=0;i<a.Length;i++)
            {
                for (int h = 0; h < m.GetLength(0); h++)
                    for (int j = 0; j < m.GetLength(1); j++)
                        
                        m[h,j] =(int)a[i]+(int)a[i+1] ;
            }
            return m;
        }