Select subset of a matrix

Two problems: 1) select a subset of a matrix in cvx_optimization, 2) take inverse of a matrix. To be concrete, I have an NAxN matrix (Theta) and I want to select N specific rows based on some constraints to get NxN matrix. My problem looks like


cvx_solver GUROBI

variable P(N) integer;

maximize –

subject to

    for i=1:N
        P(i) >= A*(i-1) + 1;
        P(i) <= i*A;
    MatR = Theta(P,:);
    u == inv(MatR)*--; (I use inv(MatR) to optimize over different variable that defines a convex objective function)        


In selecting the subset of matrix, MatR, I get the error: conversion to double from cvx is not possible. Much Appreciate any help.

inv is not supported in CVX, as it is in general not convex.