Using stddev() and log() in portfolio backtest

[traderuk99]

I'm trying to use Historical Volatility as a positionscore in my portfolio backtest. The HV formula uses Log() and stdev().

The formula works fine as an indicator, but in a backtest, positionscore rank is always zero.

I read this is due to the fact that arrays are not to be used in the 2nd phase of the BT:

Trying to use stdev in a custom metric - I get no output from stdev but others work

Below is my code for a custom metric. It works except the part where I try to get the standard deviation of my list of trades. This gives me no output at all. I don't understand what I am missing. I looped though my trades to get all the profits and losses into an array called pnl. Checking with my ami broker output pnl[1] indeed matches the first trade profit or loss output from the backtest. There are 30 trades in the backtest so I hardcoded the 30. At the bottom of the metrics output win…

However, I am clueless how to make this work in portfolio BT mode: any help appreciated please.

(...buy/sell trading system code here...)

function getHistoricalVolatility(src, periods)
{
	logret = log(src/Ref(src,-1));
	volatilityonebar = StDev(logret, periods, False);
	dv = IIf(Interval()==inWeekly, 52, 252);
	dv = IIf(Interval()==inMonthly, 12, dv);
	annualisedHV = (volatilityonebar*sqrt(dv))*100;
	return annualisedHV;
}

positionscore = getHistoricalVolatility(Close, 20);

[mradtke]

There is no problem using arrays in the second phase of the backtest. The post you referenced just shows how one can calculate standard deviation without using the built-in AmiBroker StDev() function.

I suggest you read this post: How do I debug my formula? for some ideas on how to better understand what's happening with your code and why your trades are not being taken.

[traderuk99]

Thank you mradtke.

I went through that debugging article, and using a detailed backtest report found out that I had a line buried deep in my code of:

positionscore  = IIf(positionscore<0, 0, positionscore);		

Which was creating the problem.
On removing it, the positionscore was showing as I needed it in the rank.

I must have got confused by that original article when I was searching for answers.