The *File* area displays the description of the experiment
which is actually processed by *SIESTA*. On the very left we see a
selection tree which allows the user to browse the history of an
optimization. This tree contains three branches: The
*Parameters* branch represents the history of the parameters
and how they are varied by the optimization tool. The history of the
optimization target, and the constraints of the optimization are
contained in the *Targets* branch.The *Statistics*
branch of the history tree carries information about the optimization
progress, which means the extent of the improvement that has been
achieved from one iteration to another. It displays either the
improvement of the optimization target in the case of global
optimization, or the reduction rate of the target vector's sum of
squares for inverse modeling. By selecting any of these items we
display the data in the plot area on the right-hand side of the
GUI. As in the case of an inverse modeling experiment the
optimization target is a vector of floats, a separate item will appear
in the history tree for each target vector of an iteration.

The *Statistics* give the user an idea whether the optimization
is able to achieve an improvement. If the residual reduction rate is
low, the optimization procedure is merely able to achieve any
improvement of the target. On the other hand, a high residual
reduction rate indicates a good optimization progress.

By inspecting the *Parameters* and the *Targets* section
one can track how the optimization tool changes parameters in order to
achieve an improvement and how the optimization target evolves. This
gives the user the possibility to verify his personal understanding of
the behavior of a **model** against its actual behavior. Unless the
user's personal understanding of a **model** coincides with the
optimization tool's experiences, the user should either rethink or
verify the implementation of the **model**. In this respect, the GUI
for the optimization procedure is extremely valuable. It helps to
verify the **models** and to avoid misleading optimization results.

1999-05-27