When taking derivatives with an aggregate (vector or matrix) denominator in order to find a maximum or minimum of the aggregate, it should be kept in mind that using numerator layout will produce results that are transposed with respect to the aggregate. For example, in attempting to find the maximum likelihood estimate of a multivariate normal distribution using matrix calculus, if the domain is a "k"×1 column vector, then the result using the numerator layout will be in the form of a 1×"k" row vector. Thus, either the results should be transposed at the end or the denominator layout (or mixed layout) should be used.