Question

I have two vectors, I am trying to use them in a function to return just the sample covariance.
Can anyone help me fix my program? I am new to python and programming in general.

xv= array([8., 9.5, 7.8, 4.2, -7.7, -5.4, 3.2])
yv= array([8.9, 2.0, 4.8, -4.2, 2.7, -3.4, -5.9])

def cov(x,y):
    if (len(x) != len(y)
        [Stop] 
        x.bar = mean(x) 
        y.bar = mean(y) 
        N = len(x)      
    Cov = (sum((x-x.bar)*(y-y.bar))) / (N-1.0) 
    return(Cov) 

Answer 1

Here is my version without using external libraries. The equation for covariance is from Wikipedia: http://en.wikipedia.org/wiki/Covariance

x = [8., 9.5, 7.8, 4.2, -7.7, -5.4, 3.2]
y = [8.9, 2.0, 4.8, -4.2, 2.7, -3.4, -5.9]

def mean(x):
    return sum(x) / len(x)

def cov(x, y):
    x_mean = mean(x)
    y_mean = mean(y)
    data = [(x[i] - x_mean) * (y[i] - y_mean)
            for i in range(len(x))]
    return sum(data) / (len(data) - 1)

print cov(x, y)