Detailed Instructions: You are given a passage. You need to construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) its answer is the whole paragraph. Avoid creating questions that can be answered correctly without actually understanding the paragraph.
Q: Besides large systems of equations, matrices are also useful to solve for efficient portfolios. The relationships between various asset classes are grouped in a "covariance matrix". The variance of the portfolio can be calculated using simple matrix multiplication of the covariance matrix and the allocation to the portfolio.

Also, matrices are used in optimization problems, and regression analysis.
A:
application of matrices in economics?