How to access sample (k+1)T ?

Hello, Have a look at this graph of P&0 Algorithm in MPPT. I'm actually making a function in simulink to perform it.

In this graph there are three type of samples:

1. U(k) - which can be easily accessed.
2. U(k-1) - which can be accessed and processed using 'persistent' keyword in matlab
3. U(k+1) - That's the problem. How can I access this sample? There is no forecasting involved here as we know the complete graph.

and same implies to P(k), P(k-1) and P(k+1).

Thanks in advance.

[Jan]

If the graph is known, what is the problem of simply using U(k+1)?

[Uzair Amin]

Actually, I'm taking U as an input from Solar Panel Module into a function block where I need to process above mentioned values. How can I take U(k) as an input into function? This might work.