using System;

using System.Runtime.InteropServices;

using System.Runtime.CompilerServices;

public static class Program

{

    public static void Main()

    {

        double[,] testMulti = 

        {

            { 1, 2, 3, 4 },

            { 5, 6, 7, 8 },

            { 9, 9.5f, 10, 11 },

            { 12, 13, 14.3f, 15 }

        };

​

        var singleArray = CopyArray(ref testMulti[0, 0], testMulti.Length);

        singleArray.Dump();

    }

    public static T[] CopyArray<T>(ref T start, int length)

    {

        var target = new T[length];

        var span = MemoryMarshal.CreateReadOnlySpan(ref start, length);

        span.CopyTo(target.AsSpan());

        return target;

    }

}