Spotting the wrong denominator in a Pearson correlation function.
Codepython
import math
def pearson(x, y):
n = len(x)
mx, my = sum(x) / n, sum(y) / n
cov = sum((x[i] - mx) * (y[i] - my) for i in range(n))
sx = math.sqrt(sum((x[i] - mx) ** 2 for i in range(n)))
sy = math.sqrt(sum((y[i] - my) ** 2 for i in range(n)))
return cov / (sx + sy)
print(pearson([1, 2, 3], [2, 4, 6]))