# Randomized program

A randomized policy is a distribution over the policy set, $LaTeX: X,$ that describes a policy as a random variable. This is not restricted to stochastic programs. The randomized form is called a randomized program, and it is the following semi-infinite program in response space:

$LaTeX: \max \sum_{x} w(x) f(x) : w \in W, \sum_x w(x)g(x) \le 0, \sum_x w(x)h(x) = 0,$

where $LaTeX: \textstyle W = \left \{w: X \to [0, 1]: w(x) > 0$ for finitely many $LaTeX: x \in X,$ and $LaTeX: \textstyle \sum_x w(x) = 1.$

In this form, the randomized program is an ordinary linear program if $LaTeX: X$ is finite. More generally, the definition of $LaTeX: W$ renders the summations well defined. One could interpret $LaTeX: w$ as a randomized policy: use $LaTeX: x$ with probability $LaTeX: w(x).$ A pure strategy is when $LaTeX: w(x^*) = 1$ for some $LaTeX: x^*$ (so $LaTeX: w(x)=0$ for $LaTeX: \textstyle x \ne x^*);$ otherwise, $LaTeX: w$ is called a mixed strategy.

One key fact is that the solutions to the original mathematical program (in standard form) correspond to pure strategies in this randomized form. Further, a key to the Lagrangian Strong Duality Theorem is that every mixed strategy is dominated by a pure strategy. Moreover, this underlies the Generalized Lagrange Multiplier method, and there is no loss in optimality to restrict mixed strategies to satisfy the Haar condition: $LaTeX: \textstyle \left | \{ x: w(x) > 0 \} \right | \le m+1.$