For origins, you should use:
SetOrigin(X, Y); To move the screen around.
SetSpriteFixed(sprite$, true); The sprite won't move with the virtual screen, it will always stay at the X,Y position on the pda screen. This is very usefull for user interface sprites. They always stay on the screen even though the screen origin is changed.
Matrices in PPL can be used like this:
m$ = [10, 20, [30, 40]];
ShowMessage(m$[2][1]); // 30;