1. A computer-based method comprising: electronically inputting a set of N possible investment opportunities; defining a vector space of N-dimensional vectors of all possible portfolios in the N investment opportunities, with vector elements corresponding to investment holdings in any investment portfolio; electronically receiving by a programmed computer a factor risk model defined and calibrated for all possible portfolios in the N investment opportunities, said factor risk model comprising a matrix of factor exposures, a matrix of factor covariances, and a matrix of specific covariances; electronically receiving by the programmed computer an estimate of expected investment returns defined by an N-dimensional vector whose elements may be nonzero or may be all zero; determining an original measure of portfolio performance for any possible portfolio representing investments in the N investment opportunities that is a function of the portfolio, the factor risk model, and the expected investment returns utilizing the programmed computer; defining an original portfolio optimization strategy for determining an optimized portfolio of investment holdings comprising an objective function and zero or more constraints on the portfolio in which at least the objective function or one of the constraints of the optimization strategy is a function of the optimized portfolio and the factor risk model or expected investment returns; determining an N-dimensional new factor vector so that the vector inner product of said new factor and any column of said matrix of factor exposures substantially vanishes utilizing the programmed computer; determining a modified portfolio optimization strategy in which the objective function or at least one of the constraints is altered by adding a constant times the absolute value of the vector inner product of the new factor and a portfolio determined by the modified portfolio optimization strategy raised to a power utilizing the programmed computer; computing the optimal portfolio using the modified portfolio optimization strategy utilizing the programmed computer and portfolio optimization software; and electronically outputting the optimized portfolio.