Changeset 1b64b2f for doc/userguide/userguide.xml

Timestamp:

May 8, 2017, 2:04:19 PM (8 years ago)

Author:

Frederik Heber <frederik.heber@…>

Branches:

ForceAnnealing_goodresults, ForceAnnealing_tocheck

Children:

7ee4b5

Parents:

485eea

git-author:

Frederik Heber <heber@…> (04/06/17 05:09:37)

git-committer:

Frederik Heber <frederik.heber@…> (05/08/17 14:04:19)

Message:

ForceAnnealing now uses step width according to Barzilai-Borwein method.

• this is not as good as what MPQC does but as long as Actions don't have an internal state, we cannot do anything better, e.g. a real line-search.
• removed paramater delta from optimize-structure.
• DOCU: Updated entry in user guide and noted Barzilai-Borwein method.
• TESTS: removed deltat from force annealing regression tests.

File:

• doc/userguide/userguide.xml (modified) (3 diffs)

doc/userguide/userguide.xml

@@ -2207 +2207 @@
     combines the same Actions as <emphasis role="bold">molecular-dynamics</emphasis> does. However, it
     uses the <emphasis role="bold">force-annealing</emphasis> action instead of <emphasis role="bold">verlet-integration</emphasis>.</para>
+          <remark>Because it is a MacroAction we cannot use any more elaborate 
+          line search method during the optimization. In essence, we minimize the
+          energy function that depends on the nuclei coordinates. The function is
+          non-linear and non-convex. The best choice, given that we have gradient
+          information, would be the Conjugate Gradient method (such as Fletcher-
+          Reeves which work well also for non-linear functions). However, these
+          methods perform a line search along the gradient direction which we 
+          cannot as our Actions do not contain any internal information (apart
+          from the state for Undo/Redo). Therefore, we are restricted to the
+          method of Barzilai-Borwein where no line-search is needed but that also
+          works well for high-dimensional minimization problems.</remark>
           <para>The command below performs a structure optimization of the 
     currently selected atoms (may also be a subset) for up to 100 time
@@ -2219 +2230 @@
           --order 3 \
           --distance 3. \
-          --deltat 0.5 \
           --keep-fixed-CenterOfMass 1 \
           --fragment-executable mpqc \
@@ -2227 +2237 @@
     Otherwise only two time steps would be created: the initial and
     the final one containing the optimized structure.</para>
+        <para>Because of the use of Barzilai-Borwein for computing the 
+        stepwidth  we do not need any 'deltat' parameters. If the computed
+        step width is zero, we use a default step width of 1.</para>
         </section>
         <section xml:id="dynamics.step-world-time">