Get the overapproximation of the stochastic reach set
  ============================================================================
 
  This function will compute the overapproximation of the stochastic reach
  set via Algorithm 2 in
  
       J. D. Gleason, A. P. Vinod, and M. M. K. Oishi. 2018. Lagrangian 
       Approximations for Stochastic Reachability of a Target Tube. 
       online. (2018). https://arxiv.org/abs/1810.07118
 
  Usage: See examples/lagrangianApproximations.m
    
  ============================================================================
 
  [overapprox_set, overapprox_tube] = getSReachLagUnderapprox(sys,...
        target_tube, disturbance_set)
 
  Inputs:
  -------
    sys             - LtiSystem object
    target_tube     - Tube object 
    disturbance_set - Polyhedron or SReachEllipsoid object (bounded disturbance 
                      set)
    options         - Struct of reach set options, see SReachSetOptions
 
  Outputs:
  --------
    overapprox_set - Polyhedron object for the overapproximation of the 
                     stochastic reach set
    overapprox_tube- [Available for 'VHmethod' only] Tube comprising of an
                     overapproximation of the stochastic reach sets across the
                     time horizon
 
  Notes:
  * From polyhedral computation theory (implemented here when
    options.compute_style is VHmethod), intersections and Minkowski differences
    are best performed in facet representation and Minkowski sums are best
    performed in vertex representation. However, since in this computation, all
    three operations are required, scalability of the algorithm is severly
    hampered, despite theoretical elegance.
  * Using support functions, an arbitrarily tight polytopic overapproximation of
    the set may be computed via convex optimization (linear or second order-cone
    programs).
 
  ============================================================================
 
    This function is part of the Stochastic Reachability Toolbox.
    License for the use of this function is given in
         https://sreachtools.github.io/license/