Prevent the SSN mask from changing after a given number of iterations. This
can help convergence SSN.ZERO_FREEZE
"
ast.skip"
are not included in the count
of iterations. If ssn.zero_freeze is greater than zero but less than 1.0, the SSN mask will
be frozen when the normalized change in the map between iterations drops below the
ssn.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]