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Merge pull request #5 from tomka/add-costes-auto-threshold-alternative
Add and default to regression pattern used by Costes
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,70 @@ | ||
| package algorithms; | ||
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| /** | ||
| * Try to converge a threshold based on an update value condition. If the | ||
| * update value is larger zero, the threshold is lowered by half the distance | ||
| * between the last thresholds. If the update value falls below zero or is not | ||
| * a number, the threshold is increased by such a half step. | ||
| * | ||
| * @author Tom Kazimiers | ||
| * | ||
| */ | ||
| public class BisectionStepper extends Stepper { | ||
| protected double threshold1; | ||
| protected double threshold2; | ||
| protected double thrDiff = Double.NaN; | ||
| protected int iterations = 0; | ||
| protected int maxIterations = 100; | ||
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| /** | ||
| * Initialize the bisection stepper with a start threshold and its | ||
| * last threshold | ||
| * | ||
| * @param threshold The current threshold | ||
| * @param lastThreshold The last threshold | ||
| */ | ||
| public BisectionStepper(double threshold, double lastThreshold) { | ||
| threshold1 = threshold; | ||
| threshold2 = lastThreshold; | ||
| thrDiff = Math.abs(threshold1 - threshold2); | ||
| } | ||
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| /** | ||
| * Update threshold by a bisection step. If {@value} is below zero or not | ||
| * a number, the step is made upwards. If it is above zero, the stoep is | ||
| * downwards. | ||
| */ | ||
| @Override | ||
| public void update(double value) { | ||
| // update working thresholds for next iteration | ||
| threshold2 = threshold1; | ||
| if (Double.NaN == value || value < 0) { | ||
| // we went too far, increase by the absolute half | ||
| threshold1 = threshold1 + thrDiff * 0.5; | ||
| } else if (value > 0) { | ||
| // as long as r > 0 we go half the way down | ||
| threshold1 = threshold1 - thrDiff * 0.5; | ||
| } | ||
| // Update difference to last threshold | ||
| thrDiff = Math.abs(threshold1 - threshold2); | ||
| // Update update counter | ||
| iterations++; | ||
| } | ||
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| /** | ||
| * Get current threshold. | ||
| */ | ||
| @Override | ||
| public double getValue() { | ||
| return threshold1; | ||
| } | ||
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| /** | ||
| * If the difference between both thresholds is < 1, we consider | ||
| * that as reasonable close to abort the regression. | ||
| * */ | ||
| @Override | ||
| public boolean isFinished() { | ||
| return iterations > maxIterations || thrDiff < 1.0; | ||
| } | ||
| } |
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