def norat2ret(normarr, mean, sigma, yearly=256):
    """Reform array of N(0, 1) normalized RATES into array of RETURNS.
       Arguments mean and sigma should be in decimal form.
       Argument yearly expresses frequency to be obtained.
    """
    meanly = mean / yearly
    sigmaly = sigma / yearly ** 0.5
    retarr = 1 + meanly + sigmaly * normarr
    return retarr
