Surface Evolver Newsletter no. 6

                      Surface Evolver Newsletter Number 6
                              December 16, 1993

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

Contents:
  Kelvin's partition beaten
  Ftp directory changes
  New features of version 1.93
  Bibliography



Kelvin's partition beaten:
In 1887, Lord Kelvin posed the problem of finding the partition
of space into equal volume cells minimizing the interface area.
He suggested the cell shown in twointor.fe, which is basically
the voronoi cell for a bcc lattice.  Now Robert Phelan and Denis
Weaire of Trinity College, Dublin, have found a structure using
two types of cells that has 0.3% less area than Kelvin's. Their
Evolver datafile, phelan.fe, is now included in the Evolver package.

Ftp directory changes: 

Version 1.93 is now available for ftp.  Due to a
rearrangement of The Geometry Center's ftp directory, the path
is now  pub/software/evolver/evolver.tar.Z.  There is not a Mac
version of 1.93, as I do not have access to a Mac at the moment.

When you download, please check the date on the file and be sure
it is Dec. 16 or later.  I am sending this newsletter out before
the files actually get into the ftp directory, due to my travel plans.

Also the archive now unpacks into three subdirectories: src (source code),
doc (manual), and fe (sample datafiles).

New features:

 "history" command added to print command history.  Single-letter
  commands now included in history for convenience.  But history
  does not record responses to prompts commands may issue.

  Named quantities for scalar and vector integrands over edges and 
  facets added.  Method names are edge_scalar_integral,
  facet_scalar_integral, edge_vector_integral, and facte_vector_integral.
  Example use in datafile:

     quantity zweight info_only method facet_scalar_integral global
     scalar_integrand z^2

     quantity fvec energy method facet_vector_integral global
     vector_integrand
     q1: y^2
     q2: x*z 
     q3: y^4

  Quantity names may now be used as element attributes. Value
  of total quantity must be referred to as "total quantityname".

  Command repeat counts can now be expressions.

  More internal variables for counters on command events:
  equi_count, delete_count, notch_count, dissolve_count, pop_count, 
  where_count.  These can be used in queries to make actions
  depend on the outcome of previous equiangulation, delete, notch,
  dissolve, or pop commands, or to use the number of items satisfying
  the last where clause of a command.  These variables keep their
  values until the next command of the appropriate type.

  The manual index in 1.92 was slightly off in its page numbers.
  Fixed in current manual.

  DOS version has improved graphics.  Recognizes higher resolution
  and more colors.  See evolver.doc in evolver.zip.

  Can apply named quantities to elements with SET command. For
  example, if you have defined a named quantity, say pogo, for
  facets, you could do
     set facet quantity pogo where color == red
  Unset also works.  Of course, these commands do not apply to
  quantities declared global.


Bibliography

  D. Weaire and R. Phelan, "A counter-example to Kelvin's conjecture
  on minimal surfaces", preprint.

  X. Michalet, D. Bensimon,a nd B. Fourcade, "Fluctuating vesicles
  of high topology", to appear in Physical Review Letters.
  Uses Evolver with squared mean curvature energy to model
  elastic cell membranes.


Have a Merry Solstice and a Happy Perihelion!

End of Evolver Newsletter 6