Inverse

In the Inverse tab the desired solver for the inverse simulation can be selected and the appropriate numerical parameters can be specified. For the solver for the forward simulation see Forward.

Note

Usually the default values should not be changed. Figure 42. Numerical parameters dialog, Inverse tab

Item

Description

Inverse solver, Preconditioner

Determines which solver will be used in inverse simulation, see Linear system equations solvers , default is GSSV.

The default preconditioner is ILU.

Parameters

Specifies the parameters for the selected solver:

• Maximal inner iterations

Number of maximal allowed iterations needed to solve one linear system of equations ( “inner iterations” ), integer number, default is 1000 (iterative solvers only).

• Controller relaxation factor

If the controller adjusts the power of a heater, it will apply only this fraction of all modifications. Real number between 0 and 1, default is 0.5.

• Regularization parameter

This positive parameter determines how strong the heater power is taken into account in the quadratic cost function that has to be minimized in order to fulfill the temperature constraints. Real number, default is 1e-06.

• Start controller at

The controller starts to work when the temperature residuum is below the given value. Real number, default is 0.005.

• Minimum power criterion

This parameter is used as one abortion criterion for inverse simulations. Once the norm of the residual of the energy equation has fallen below the specified value, it is investigated whether the required values at the control points are reached. If this is not the case, the user gets the corresponding information in the terminal. Now, it is investigated whether the maximum power change is smaller than the value of the minimum power criterion. If this is the case, the computations are stopped, even the temperature values at the control points are out of the specified tolerance. The idea is that nothing is changing anymore. The default value for the minimum power criterion is 1.e-6 and SHOULD NORMALLY NOT BE CHANGED.

Update sensitivity matrix

Two conditions for updating the sensitivity matrix for the controller can be specified:

• T-norm-change

Relative change of the residuum of the temperature equation at which the sensitivity matrix will be updated. Real number, default is 0.1.

• Number of steps

Number of steps after which the sensitivity matrix for the controller will be in any case updated. Integer number, default is 10.

Controller

There are two controllers available in CrysMAS:

• constrained

Selects the more recent controller which respects power limits for the heaters and allows tolerances for the control points (default).

• unconstrained

Reactivates the old controller, which is more stable in some situation.