Find longest line without any intersection

AFL Programming
#1

I want to find the longest line that can be drawn connecting the highs of any two bars that are within the given range. see the chart below

Longest_Line_In_Range

#2

So a brute force algorithm for this would look something like:

for i = start to end // i represents the first bar of the longest bar
for j = i to end // j represents the second bar of the longest bar
  hi = H[i], hj = Hj[j]
  length = distance(hi, hj) // using pythagoras you can find the length of the line
  intersects = isLineIntersecting(i, j)
  if (!intersects && length > longest) 
    longest = length, longestStart = i, longestEnd = j

function distance(a, b) 
  sqrt((bx-ax)^2 + (by-ay)^2) // normalise, absolute value, use pythagoras to get length

// to find whether a line intersects any bar inbetween, calculate for each bar, whether that bar's y value
// is lower than the candle's highest, if so, then the candle extends above the line and thus intersects.
function isLineIntersecting(startBar, endBar)
  isLineBroken = 0;
  for i from startBar to endBar
    isLineBroken &= H[i] > m*i + b // work out what m, b is in y = mx + b

  return isLineBroken

Hope that puts you in the right direction.

#3

Thanks. I have code that uses nested loops (two for loops from 1 to maxlengthofpattern). But it slows down my afl. I am looking for some clever stuff.

#4

That's a completely different question though...

If you are hitting performance issues on a time consuming algorithm, you can either run it as a once off by storing it via a StaticVarSet or use Status("first/lastvisiblebarindex") to restrict the algo to only run on your visible bars.

eg, I only run my trade system when I click it or if I toggle the "realtime signals" to true.
When "realtime signals" is true, the chart lags in seconds as it goes over 100k bars. When I run it once and load via static var, there is no lag at all.

isRunSystem = ParamTrigger("Generate signals", "Start") || ParamToggle("Realtime generate signals", "No|Yes", 0);

if (isRunSystem) 
{
	trades = threeLH_init(0, BarCount-1);
	trade_init(trades);
	trade_rehydrateBuySell();
}

// Otherwise, I just load it from the static vars

procedure threeLH_load() {
	local nSignals;

	g_3lh_signals = StaticVarGet("g_3lh_signals");
	g_3lh_trades = StaticVarGet("g_3lh_trades");
}

If you want help to optimise your algo, you'd have a better chance of someone putting their time to helping you, if you showed your loops so readers can see what time complexity it's running in.

1 Like
#5

@AlgoEnthusiast, if nested loops are the only way to do it, to achieve a much faster execution time, you should convert your AFL code to a DLL function using the free Amibroker Development Kit (ADK)

(It requires the knowledge to code and compile a DLL using Microsoft C++.)

See this kb article and/or search the forum for additional topics about its usage.

#6

@AlgoEnthusiast - post the code. Discussion about code is pointless without the code.

Please follow this advice: How to ask a good question