The Laguerre Filter Adaptive (LFA) was authored by John Ehlers. The LFA requires the highest and lowest of the difference of current price and previous price, some averaging, and a good deal of feedback to fill its calculation. The user may change the input (midpoint) and the period lengths. This indicator’s definition is further expressed in the condensed code given in the calculation below.

The Laguerre Filter Adaptive is a trend indicator and may be used in conjunction with other studies. No trading signals are calculated.

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### Calculation

//input = price, user defined, default is midpoint
//period1 = p1 = user defined, default is 20
//period2 = p2 = user defined, default is 5
//abs = function, returns absolute value of argument
//median = function, returns price at middle of period
//diff = difference, prev = previous
//index = current bar number

```prevF = ifNull(price, filt[index-1]);
diff = Math.abs(price - prevF);
hh = highest(p1, DIFF);
ll = lowest(p1, DIFF);
if (hh - ll != 0) mid = (diff-ll) / (hh - ll);
if (hh - ll != 0)
alpha = median(p2, MID);  //returns price at middle of p2
endIf
prevL0 = ifNull(price, LO[index-1]);
prevL1 = ifNull(price, L1[index-1]);
prevL2 = ifNull(price, L2[index-1]);
prevL3 = ifNull(price, L3[index-1]);
l0 = alpha*price + (1-alpha)*prevL0;
l1 = -(1 - alpha)*l0 + prevL0 + (1 - alpha)*prevL1;
l2 = -(1 - alpha)*l1 + prevL1 + (1 - alpha)*prevL2;
l3 = -(1 - alpha)*l2 + prevL2 + (1 - alpha)*prevL3;
Plot: filt = (l0 + 2*l1 + 2*l2 + l3) / 6;```