Help specify cTx objectives for mincx solver
[V1,...,Vk] = defcx(lmisys,n,X1,...,Xk)
defcx is useful to derive the c vector needed by
mincx when the objective is expressed in terms of the matrix variables.
Given the identifiers
X1,...,Xk of the matrix variables involved in this objective,
defcx returns the values
V1,...,Vk of these variables when the n-th decision variable is set to one and all others to zero.