Parameters for minimization algorithm

• ahfinder::ahf_tol
  Sets the tolerance for the minimization algorithm. The default value is 0.1.
• ahfinder::ahf_maxiter
  Sets the maximum number if iterations for each step of the POWELL algorithm. The default value is 10.
• ahfinder::ahf_minarea
  Usually the square of the expansion is minimized. To switch to minimization of the area one can use ahf_minarea = "yes" (default is "no"). Notice that only for time symmetric data the surface found by area minimization will correspond to an apparent horizon.