Flowsheet Optimizer Step Sizes Window
This window allows you to select a relative minimum step size for each variable; the default value is 0.001 (0.1%). When all variables change less than their minimum, the optimizer has converged. You may also limit the amount a variable can change at each calculational cycle by entering an absolute maximum step size.
The optimizer calculates derivatives using finite differences. The value of each variable, in turn, is perturbed by some small amount and the flowsheet is resolved. The differences between the base case solution and the perturbation solution are used to approximate the derivatives. By default, the perturbation for each value is calculated at every optimization cycle as 1% of the variable's current value. You can override this default by providing an alternate relative step size or an absolute step size. If the value of a variable is close to zero, using a relative perturbation may cause excessively small steps to be used. In these cases, it is generally preferable to use an absolute perturbation step size corresponding to 1% of the typical value of the variable.