>>>> STEP: max_step
all third-level commands in block > PARAMETER
This command defines the maximum allowable step size, limiting the change in the corresponding parameter per iTOUGH2 iteration. Large steps are usually proposed for a parameter if
(i) the initial guess is far away from the best estimate;
(ii) the parameter has a low sensitivity, or
(iii) the parameter is highly correlated to more sensitive parameters.
If the system state is a strongly non-linear function of the parameter, even a moderate step size may make the inversion unstable. Parameter max_step should be chosen large enough, so that the proposed step size |deltpa(p’)| is reduced to |delta(pmax)| only during the first few iterations. The figure below illustrates that limiting the step size also changes the direction of the step taken in the parameter space. A global step size limitation can also be specified (see command >>> STEP), maintaining the direction of vector delta(p).
>>> MATERIAL: SANDY
>>>> standard DEVIATION: 0.10
>>>> max. STEP size : 0.05