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 span = testMulti.AsSpan<double>();

        var singleArray = new double[span.Length];

        span.CopyTo(singleArray.AsSpan());

        singleArray.Dump();

    }

    public static Span<T> AsSpan<T>(this Array array)

    {

        return MemoryMarshal.CreateSpan(ref Unsafe.As<byte, T>(ref MemoryMarshal.GetArrayDataReference(array)), array.Length);

    }

}