just trying to follow a formula.
the equation starts of as follows,
1 = sum( xi * (cov(ri, r) / sigma^2(r) ) please note i's are subscripts
then next line is the following
1 = sum( (1/sigma(r)) * xi * sigmai * p(ri, r) p is the correlation coeff
I cannot get the second line, sure I'm being stupid and missing something very obvious!
Note that $$\rho(r_i,r)= \frac{\text{cov}(r_i,r)}{\sigma(r_i)\cdot \sigma(r)}\\\implies \text{cov}(r_i,r) = \rho(r_i,r)\cdot \sigma(r_i)\cdot \sigma(r)$$