Как найти f (t-1), если f (t) задано с помощью simulink

  public class AddingThisAddingThat 
    {

        private int carry = 0;        
        public byte[] AddRecursive(byte[] a, byte[] b)
        {
            //Start from bottom of the byte[] array
            a = a.Reverse().ToArray();
            b = b.Reverse().ToArray();
            if (a.Length == 0) return new byte[] { };            
            int tempresult = a[0] + b[0] + carry;
            byte[] z = new byte[]
            { (byte)(tempresult) };
            carry = tempresult / (byte.MaxValue + 1);
            return z.Concat(AddRecursive(a.Skip(1).ToArray(), b.Skip(1).ToArray())).ToArray();
        }


    }

 public void TestSetup()
        {
            addthisaddthat = new AddingThisAddingThat();
        }

        [Test]
        public void Add_UsingARecursiveAlgorithm_ValuesAreAdded()
        {
            //First Test
            byte[] expectedResult = addthisaddthat.AddRecursive(new byte[] { 1, 1, 1 }, new byte[] { 1, 1, 1 }).Reverse().ToArray();
            Assert.That(expectedResult, Is.EqualTo(new byte[] { 2, 2, 2 }));
            //Sec Test
            expectedResult = addthisaddthat.AddRecursive(new byte[] { 1, 1, 255 }, new byte[] { 0, 0, 1 }).Reverse().ToArray();
            Assert.That(expectedResult, Is.EqualTo(new byte[] { 1, 2, 0 }));
            //Third Test
            expectedResult = addthisaddthat.AddRecursive(new byte[] { 255, 255, 255 }, new byte[] { 255, 255, 255 }).Reverse().ToArray();
            Assert.That(expectedResult, Is.EqualTo(new byte[] { 255, 255, 254 }));
        }

        [OneTimeTearDown]
        public void TestTearDown()
        {
            addthisaddthat = null;
        }