However, comparing the two root node searches, I found some aspects where Onno's root node search might be better (or in other words, Stockfish's root node search looks strange).

1. Stockfish re-orders the moves at root node by the MovePicker at every depth. This would only make sense if MovePicker is a better heuristic than the order we already have. Note that the order we already have was initialized by a depth 1 search (which is btw wasted if we re-order at every depth), and then modified by moving PV moves to the head. My intuition is that the latter move ordering is the better one. I did a test where I removed the reordering by MovePicker at root node from Stockfish. Differences in playing strength were not measurable, but at least the results indicate that I am not completely wrong. (Without re-ordering did 3 Elo better, at an error margin of 18 Elo.)

2. Stockfish does not do windowing in MultiPV mode. Onno does. One window for all PV moves is likely to be a bad idea; not windowing at all is the simplest solution. Onno chooses separate windows for each move. I did not compare the approaches empirically and am not planning to do so (as I have little interest in MultiPV).

3. Stockfish's alpha modification in MultiPV mode looks like a hack, and it most likely is.

Code: Select all

```
while (move=get_next_move())
{
// Aspiration window is disabled in multi-pv case
if (Root && MultiPV > 1)
alpha = -VALUE_INFINITE;
...
// Update alpha. In multi-pv we don't use aspiration window, so
// set alpha equal to minimum score among the PV lines.
if (MultiPV > 1)
alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
else if (value > alpha)
alpha = value;
}
```

The correct way to handle this should be:

1. As we don't have windowing at root node, alpha=-VALUE_INFINITE comes in and is used for the first move anyway.

2. Instead of the FIXME line set alpha in the following way for any value of MultiPV:

Code: Select all

```
if (moveCount >= MultiPV)
alpha = Rml[MultiPV-1].pv_score;
```

Above changes are not tested.