# Tag Info

## Hot answers tagged portfolio-theory

6

Let $R$ be a random vector of risky returns and let $r_f$ denote the risk free rate. Let vector of expected returns $\boldsymbol{\mu} = \operatorname{E}[R]$ and covariance matrix $\Sigma = \operatorname{Cov}(R)$. The maximum Sharpe ratio portfolio among risky assets is called the tangency portfolio. Quick method to tangency portfolio Let's find the ...

6

To complement @skoestimeier's answer on the shortselling-allowed case, I provide a vectorised version. Using the original notation in my post (you may change $r$ to something like $r-r_f$, but this doesn't affect the algebraic structure). Our goal is to find the maximiser for the problem $$\max_{w}f(w):=\frac{w^T r}{(w^T\Sigma w)^{1/2}}.$$ Let $$\phi: w\... 5 There are two cases, where short sales are allowed: With riskless lending and borrowing and without. As mentioned in the comments, you just have to solve a linear system. With riskless lending and borrowing The existence of a riskless lending and borrowing rate r_f implies that there is a single portfolio of risky assets, that is preferred to all other ... 4 Trying to shed some light here: What we also see using this here, is that if returns are log-normally distributed, ie.$$ 1 + r = \exp(\mu + \sigma Z), $$with Z standard-normal, then$$ E[1+r] = \exp(\mu + \frac 12 \sigma^2) $$holds. But the geometric mean GM is given by \exp(\mu) and we have$$ \log(GM) = \mu = \log(E[1+r]) - \sigma^2 /2  and ...

3

This will depend on the definition of "return on the long run". If we define the annualized return on the long run by $\frac{1}{T}\ln \frac{S_T}{S_0}$ for a certain time $T$ in the future, then \begin{align*} E\left( \frac{1}{T}\ln \frac{S_T}{S_0} \right) = \mu-\frac{1}{2}\sigma^2, \end{align*} as claimed. Note that $\mu$ is the instant, or instantaneous, ...

3

You are absolutely right that no one would like to replicate return of risk free assets when such instrument is easily available in the market and can be bought directly. So, why financial managers put their time and energy in creating such risk free portfolio? The application of creating risk free portfolio is mostly used in pricing derivative securities. ...

1

SPT refines MPT by introducing the notion of stochastic variation into expected returns, whereby allocators can determine optimal bet sizes that maximize the long-run rate of return. Previously, under MPT, allocators operated under the assumption that the mean rate of return would equivocate to the expected long run logarithmic rate. SPT refines this ...

1

I think the goal of the exercise is to create some sort of risk-free portfolio with a positive return after borrowing costs. Then, theoretically, you can lever it up. And of course, at 10x leverage, you should be pretty sure that is really is risk-free.

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