% mfile MoveSharkRight
% decide whether to move sharks right, move, mark as having moved, and update boundaries
% decide whether sharks can move right
  move( 2:d+1, 1:d+1 ) = shark( 2:d+1, 1:d+1 ) & ...
          ( sharkdir( 2:d+1, 1:d+1 ) == 1) & ( ~shark( 2:d+1, 2:d+2 ) );
% decide whether sharks can eat
  eat( 2:d+1, 1:d+1 ) = move( 2:d+1, 1:d+1 ) & fish( 2:d+1, 2:d+2 );
% decide whether sharks can breed
  sbreed ( 2:d+1, 1:d+1 ) = ( sharkage(  2:d+1, 1:d+1 ) > SBREED ) & ...
          move( 2:d+1, 1:d+1 );
% update shark positions
  shark( 2:d+1, 2:d+1 ) = ( shark( 2:d+1, 2:d+1 ) & (~move( 2:d+1, 2:d+1 )))|...
          move( 2:d+1, 1:d ) | sbreed( 2:d+1, 2:d+1 ) ;
% update shark ages
  sharkage( 2:d+1, 2:d+1 ) = ( sharkage( 2:d+1, 2:d+1 ) .* ...
                             (~move( 2:d+1, 2:d+1 )) ...
                               .* shark( 2:d+1, 2:d+1 ) ) + ...
                             ( sharkage( 2:d+1, 1:d   ) .* move( 2:d+1, 1:d ) );
% update time since sharks' last meal
  sharkeat( 2:d+1, 2:d+1 ) = ( sharkeat( 2:d+1, 2:d+1 ) .* ...
                             (~move( 2:d+1, 2:d+1 )) ) + ...
                             ( sharkeat( 2:d+1, 1:d   ) .* ...
                             ( move( 2:d+1, 1:d ) & (~eat( 2:d+1, 1:d )) ) );
% mark shark as having moved
  sharkdir( 2:d+1, 2:d+1 ) = sharkdir( 2:d+1, 2:d+1 ) .* ...
                          ( ~move( 2:d+1, 1:d )) .* ...
                          (sharkdir( 2:d+1, 2:d+1 ) ~= 1);
% update (eaten) fish positions
  fish( 2:d+1, 2:d+1 ) = fish( 2:d+1, 2:d+1 ) & (~shark( 2:d+1, 2:d+1 ) );
% update (eaten) fish ages
  fishage( 2:d+1, 2:d+1 ) = fishage( 2:d+1, 2:d+1 ) .* (~shark( 2:d+1, 2:d+1 ));
  UpdateBoundaries;
  if dbug == 1, 
      subplot(221), plotsharkfish;
      disp(['i= ',num2str(i),' just moved right']), keyboard, 
  end