def METHOD_NAME(a,b,m):
    MolWt = sum(m)
    sum1 = 0.0
    sum2 = 0.0
    sum3 = 0.0
    for i,rows in enumerate(m):
        sum1 = sum1 + m[i]*a[i]*b[i]
        sum2 = sum2 + m[i]*a[i]
        sum3 = sum3 + m[i]*b[i]
    Iab = -sum1 + 1.0/MolWt*sum2*sum3
    return Iab