```
#
# TD Ameritrade IP Company, Inc. (c) 2008-2019 ParabolicSAR
# Changed to 4 hour aggregation by Horserider 12/13/2019
input accelerationFactor = 0.02;
input accelerationLimit = 0.2;
Assert(accelerationFactor > 0, "'acceleration factor' must be positive: " + accelerationFactor);
Assert(accelerationLimit >= accelerationFactor, "'acceleration limit' (" + accelerationLimit + ") must be greater than or equal to 'acceleration factor' (" + accelerationFactor + ")");
def state = {default init, long, short};
def extreme;
def SAR;
def acc;
input agg = AggregationPeriod.FOUR_HOURS;
def high = high (period = agg);
def low = low (period = agg);
switch (state[1]) {
case init:
state = state.long;
acc = accelerationFactor;
extreme = high;
SAR = low;
case short:
if (SAR[1] < high)
then {
state = state.long;
acc = accelerationFactor;
extreme = high;
SAR = extreme[1];
} else {
state = state.short;
if (low < extreme[1])
then {
acc = Min(acc[1] + accelerationFactor, accelerationLimit);
extreme = low;
} else {
acc = acc[1];
extreme = extreme[1];
}
SAR = Max(Max(high, high[1]), SAR[1] + acc * (extreme - SAR[1]));
}
case long:
if (SAR[1] > low)
then {
state = state.short;
acc = accelerationFactor;
extreme = low;
SAR = extreme[1];
} else {
state = state.long;
if (high > extreme[1])
then {
acc = Min(acc[1] + accelerationFactor, accelerationLimit);
extreme = high;
} else {
acc = acc[1];
extreme = extreme[1];
}
SAR = Min(Min(low, low[1]), SAR[1] + acc * (extreme - SAR[1]));
}
}
plot parSAR = SAR;
parSAR.SetPaintingStrategy(PaintingStrategy.POINTS);
parSAR.SetDefaultColor(GetColor(5));
```