Surface Evolver Newsletter no. 12

                    Surface Evolver Newsletter Number 12
                              July 19, 1995

                   Editor: Ken Brakke, brakke@geom.umn.edu

Contents
  Version 1.99 ready
  New features

Version 1.99 ready.
  Surface Evolver version 1.99 is now available from geom.umn.edu
  in /pub/software/evolver/evolver.tar.Z.  There are also new DOS and 
  Mac versions.  The DOS version is in evolver.zip.
  The Mac version is in Evolver.sea.Hqx.  This was compiled for
  use with a math coprocessor and will not run on a Power Mac.
  There is a non-coprocessor version in Evolver.no68881.sea.Hqx
  which will run on the Power Mac I have access to, although it has
  been reported to crash others. Any ambitious volunteers to figure
  this out will be welcomed.
 
  For those of you into Hessians and eigenvalues, there is a little
  tutorial in eigentut.txt.  This is a plain text file, about 10 pages.


New features.

  Storage used by element structures has been cut down by only
  allocating storage for features actually used.

  The limit on the number of constraints has been raised to 128,
  and can easily go much higher if somebody needs it.

  Body "volume" technically should be a read-only value, the
  actual computed volume.  "target" should be used for setting
  the volume constraint, as in "set body[1] target 2.34", 
  although "set body[1] volume 2.34" will still work, although
  with a warning.

  "volconst" has been added as a read-write body attribute.
  This is a constant added to the calculated volume.  Also
  applies to named quantities.

  The command "convert_to_quantities" will do an automatic
  conversion of old-style energies to new-style named quantities.
  This has the same effect as the -q command line option, but
  can be done from the Evolver command prompt.  Useful when
  "hessian" complains about not being able to do a type of energy.
  A few energies don't convert yet.  It is my intention that
  this will be the default in the near future, probably in 
  version 2.00.

  "edgeswap" command will force an equiangulation-type switch
  on designated edges, as in "edgeswap edge[23]" or
  "edgeswap edge where color == red".  "edgeswap edge" will
  swap all edges, if you like to see weird surfaces.

  A "variable_parameter" is a parameter whose value will be varied
  during optimization.  Just use "variable_parameter" instead of
  "parameter" in the top of the datafile.  Be aware that energy
  derivatives with respect to variable parameters are done
  numerically, not symbolically.  Won't work with Hessian yet.

  For the torus mode, torus translations have been automatically
  added as view_transform_generators after any appearing in the
  datafile.  So multiple copies of the fundamental domain can
  been seen with
      transform_expr "abc"

  Command P can now take a number after it, so "P 8" starts geomview
  without having to bring up the "P" menu.

  "saddle" and "hessian_seek" commands takes maximum stepsize, 
  e.g. "saddle 0.5".

  "move" command will continue in direction of previous motion,
  whether from gradient or hessian.  Takes stepsize, e.g. "move 0.5".
  Negative move is not a perfect undo.

  Toggles print previous value along with new value.

  Can now make saddle or hessian_seek minimize squared gradient
  instead of energy.  Use hessian_menu toggle G.

  There is now a "bottominfo" command that prints out the bottom
  part of a dumpfile.  Useful for generating new datafiles from old.

  You can redefine single-letter commands with " x :::= command".
  Restore with "x :::= ".  Redefs undone at start of surface.
  Redef not retroactive to single letter commands used in
  definition of commands. Letter redefed at execution, not parsing.
  Redefed letter used in command will revert to standard meaning
  when letter unredefed. Meant for analogous replacements,
  like special r.  "r :::= { hooke_length := hooke_length/2; r}"
  will work right first time, but not second. Use single quotes
  around letter to get old meaning, i.e. 'r'.
  Should only use to disable commands.

  hessian_menu has option Z to do subspace iteration for multiple
  eigenvectors (same as "ritz" command), and you can pick
  eigenvectors for motion with option X.

  Read-only variable "last_eigenvalue" stores eigenvalue found
  in saddle command, or first eigenvalue found by ritz.
  Read-only variable "last_hessian_scale" stores stepsize used
  by most recent saddle or hessian_seek command.

  Compilation option -DSDIM=3 will hard-wire space dimension 3 into
  the code, permitting more compiler optimization.  But such
  an Evolver cannot handle any other space dimension.

  The eigenprobe command has an alternate form, eigenprobe(value,iters),
  that will do shifted inverse power iteration to find the eigenvalue
  nearest the given value. iters is the limit on the number of iterations.
  The eigenvalue is stored in last_eigenvalue, and the eigenvector
  can be used via the "move" command.