perturb setting

The perturb setting is a boolean expression, specifying whether the perturbation equations in a fractal formula can be used in combination with the current parameter values. This value defaults to true if not present.

Often, for example with the standard Mandelbrot formula, not all combinations of parameter values will work with perturbation calculations. This setting should return false for the parameter values that are not supported, so regular arbitrary precision calculations will be used instead.

The expression for the perturb setting must only use constant values, including the values of parameters and most predefined symbols. It is re-evaluated every time a parameter changes, or when one or more of the predefined symbols are changed.

The perturb setting can be used in the default section of fractal formulas.

Here is a snippet taken from the Mandelbrot formula. This formula has a complex power parameter that can be any value, but perturbation calculations are only supported for power values of 2, 3 and 4:

default:
  perturb = @power == (2, 0) || @power == (3, 0) || @power == (4, 0)