Example 20F ASM Manual - Risk Free Portfolios

jeudi 5 mars 2015

A non-dividend paying stock's price follows the Ito process:

dS(t) / S(t) = .12dt +.3dZ(t)



Another non-dividend paying stock has a price which follows the Ito process:

dQ(t)/Q(t) = .3dt +.9 dZ(t)



S(0)=40

Q(0)=5



A risk-free portfolio requiring no cash outlay consists of 100 shares of S and x shares of Q, and a bond of value K earning the risk-free rate.

Determine x.



Answer: This time we'll arrange for the dZ(t) coefficients to add up to 0. Since we want to cancel out dZ(t), we need to sell an amount of Q having 1/3 the value of the amount of S that we own. Since we own 100(40)=4,000 of S, we need to sell Q having a value of 4000/3, which means

x=-800/3.



Can someone please explain to me the formulas used to solve this? I am not understanding how x was found.





Example 20F ASM Manual - Risk Free Portfolios

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