[amibroker] CBT / maintain net exposure close to zero

["cdepuy" <cdepuy@xxxxxxxxx>]

I am trying to figure out how to get the custom backtester to take 
only buy signals when greater than 5% net short and take only short 
signals when I'm greater than 5% long.  I recognize that is not the 
best feedback loop required to maintain a "hedge" but for learning 
purposes, I'm OK with an approximation.  There are examples of how 
to trade based on a built in calculation of Equity, but there's 
apparently no canned way to calculate Longs - Minus Shorts (net 
dollar exposure), or similar.

I cannot figure out why this code below does not only take buy 
trades when I'm short.

I've put this together using the Houston slides, plus the 01-2005 
newsletter and http://www.amibroker.com/library/detail.php?id=934:

SetOption("UseCustomBacktestProc", True );
Tradesize = 10;
net=0;
if( Status("action") == actionPortfolio )
{
 bo = GetBacktesterObject();
 bo.PreProcess(); // Initialize backtester
 for(bar=1; bar < BarCount; bar++)  //i set this to bar=1 instead of 
zero to prevent bar-1 from goign out of subscript range error
 {
  bo.ProcessTradeSignals( bar );
  CurEquity = bo.Equity;
  for( pos = bo.GetFirstOpenPos(); pos; pos = bo.GetNextOpenPos() )
  {
   posval = pos.GetPositionValue();

	if(pos.islong == -1){LongOrShort = 1;}if(pos.islong == 0)
{LongOrShort = -1;}
	net = net+ pos.GetPositionValue() * LongOrShort;

   diff = posval - 0.05 * CurEquity;
   price = pos.GetPrice( bar, "O" );
   // rebalance only if difference between desired and
   // current position value is greater than 0.5% of equity
   // and greater than price of single share

for (trade=bo.GetFirstOpenPos(); trade; trade = bo.GetnextOpenPos())
	{//loop through all open positions	

   if( net[bar - 1] > .05 )
   {
	scalesize = trade.getentryvalue() * 2;
    bo.ScaleTrade( bar, pos.Symbol, net[bar-1] > .05, price, 
Scalesize);
   }

   if( net[bar - 1] < -.05 )
   {
	scalesize = trade.getentryvalue() * .5;
    bo.ScaleTrade( bar, pos.Symbol, net[bar-1] < -.05, price, 
scalesize);
   }
//	bo.UpdateStats(bar,2);
//	trade.addcustommetric("net",net);

	} // end of for loop over trades at this bar
  }
 }
 bo.PostProcess(); // Finalize backtester
}

Buy=Cover=C > MA(C,500);
Sell=Short=C < MA(C,500);


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