gistfile1.py

def pagerank(matrix, d_factor=0.85):
    """
    Calculate the pagerank vector of a given adjacency matrix (using
    the power method).

    :param matrix: an adjacency matrix
    :param d_factor: the damping factor
    """
    size = len(matrix)
    epsilon = 0.0001
    matrix = matrix.copy()

    # Divide each column by its number of outgoing links
    for i in xrange(0, size):
        col_sum = matrix[:,i].sum()
        if col_sum:
            matrix[:,i] /= col_sum

    e = ((1.0 - d_factor) / size) * numpy.ones((size, size))
    matrix = d_factor * matrix + e

    result = numpy.ones(size) / size
    prev = numpy.ones(size) / size
    iteration = 0

    while True:
        result = numpy.dot(matrix, result)
        result /= result.sum()
        diff = numpy.abs(result - prev).sum()
        print "Iteration %d, change %f" % (iteration, diff)
        if diff < epsilon:
            break
        prev = result
        iteration += 1

    return result