Prevent the AST mask from changing after a given number of iterations. This can help
convergence AST.ZERO_FREEZE
"
ast.skip"
are not included in the count of iterations. If ast.zero_freeze is greater than zero but less
than 1.0, the AST mask will be frozen when the normalized change in the map between iterations
drops below the ast.zero_freeze value. A value less than zero means that the mask is frozen as soon
as the initial iterations specified by parameter "
ast.skip"
have been done. A value equal to zero
means that the mask is never frozen. [0.0]