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Fundamentals of creating a diversified portfolio based on numbers?
Your question is a complex one because knowledge of the investor's beliefs about the market is required.  For almost any quantitative portfolio, one must have a good estimate of the expected return vector and covariance matrix of the assets in question.  The expected return vector, in particular, is far from estimable.  No one agrees on it and there is no way to know who is right and who is wrong. In a world satisfying the conditions of the CAPM, you can bypass this problem because the main implication of the CAPM is that the market weights are optimal.  In that case the answer to your question is that you should determine the market weights of the various assets and use those along with saving in a risk-free account or borrowing, depending on your risk tolerance.  This portfolio has the added benefit that you don't need to rebalance much...the weights in your portfolio adjust at the same rate as the market weights. Any portfolio that has something besides this also includes some notion of expected return aside from CAPM fair pricing.  The question for you, then, is whether you have such a notion.  If you do, you can mix your information with the market weights to come up with a portfolio.  This is what the Black-Litterman method does, for example: get the expected return vector implied by market weights and the covariance matrix, mix with your expected return vector, then use mean-variance optimization to come up with your final weights.