private static Split findBestSplit(float[] sortedValues, float min_rd, int min_y, int NCount, int numThresholds)
{
int YCount = sortedValues.Length;
float min = sortedValues[0];
float max = sortedValues[sortedValues.Length - 1];
float thresholdInterval = (max - min) / (numThresholds + 1);
float NInterval = (float)NCount / (numThresholds + 1);
int[] YCountLeft = new int[numThresholds + 1];
int[] NCountLeft = new int[numThresholds + 1];
int[] YCountRight = new int[numThresholds];
int[] NCountRight = new int[numThresholds];
float[] thresholds = new float[numThresholds];
float threshold = min + thresholdInterval;
float NLeft = NInterval;
int YLeft = 0;
int YRight = YCount;
for (int i = 0; i < numThresholds; i++)
{
thresholds[i] = threshold;
for (; sortedValues[YLeft] < threshold; YLeft++, YRight--)
{
;
}
YCountLeft[i] = YLeft;
YCountRight[i] = YRight;
NCountLeft[i] = (int)NLeft;
NCountRight[i] = NCount - (int)NLeft;
threshold += thresholdInterval;
NLeft += NInterval;
}
YCountLeft[numThresholds] = YCount;
NCountLeft[numThresholds] = NCount;
Split best = new Split {
Score = float.MinValue
};
for (int i = 0; i < numThresholds; i++)
{
if (YCountLeft[i] < min_y)
{
continue;
}
float left_rd = (float)YCountLeft[i] / Math.Max(NCountLeft[i], 1);
for (int j = i + 1; j < numThresholds; j++)
{
if (YCountRight[i] < min_y)
{
continue;
}
float right_rd = (float)YCountRight[i] / Math.Max(NCountRight[i], 1);
float middleY = YCountLeft[j] - YCountLeft[i];
float middleN = Math.Max(NCountLeft[j] - NCountLeft[i], 1);
float middle_rd = middleY / middleN;
if (middle_rd < min_rd)
{
Split test = new Split {
Score = left_rd + right_rd - middle_rd
};
if (test.Score > best.Score)
{
if (j - i > 3)
{
float[] density = new float[j - i];
for (int k = 0; k < density.Length; k++)
{
density[k] = (float)(YCountLeft[i + k + 1] - YCountLeft[i + k]) / (NCountLeft[i + k + 1] - NCountLeft[i + k]);
}
density = Gaussian.Convolve(density, 1);
int minIndex = density.MinIndex();
test.Threshold = thresholds[i + minIndex];
}
else
{
test.Threshold = (thresholds[i] + thresholds[j]) / 2;
}
test.NLeft = (int)(((test.Threshold - min) * NCount) / (max - min));
best = test;
}
}
}
}
return(best);
}
