# Surface Evolver Newsletter no. 9

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                          Surface Evolver Newsletter Number 9
                                  September 30, 1994

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

    Version 1.96 is now available.

    New features:

       Indexing can be done on element generators in commands.  That is, you
       can say "list vertex[23]" instead of "list vertex where id==23".
       The new syntax avoids searching through the entire element list for just
       one element. You can also apply indices to component elements, as
       in "foreach edge ee do print ee.vertex[1].id".  Component elements are
       accessed by linear search through a list, but the list is usually short.
       Remember indices start at 1.

       Named quantities can be composed of arbitrary functions of method instances,
       instead of just sums.  The keyword "function" indicates this.  Example:
       method_instance inst_1 method edge_length global
       method_instance inst_2 method vertex_scalar_integral global
       scalar_integrand x^2-y*z
       quantity comp energy function inst_1^2 + sin(inst_2)

       Named quantities may refer to element attributes in expressions for
       integrands. This can give more discriminating control over quantities
       on different elements, by using facet densities in integrands for
       example.  This feature is especially useful with `extra' attributes,
       which are added completely under the user's control.

       Hessian: Newton's Method can greatly accelerate convergence to a minimum,
       but users of the "hessian" command know that one has to be extremely
       close to the minimum before the command works.  This is largely due
       to motions tangential to the surface as the triangulation rearranges itself.
       There is now a toggle "hessian_normal" that constrains motion to be along
       the surface normal (volume gradient, to be precise).  Points without
       a well-defined normal (such as along triple junctions or at tetrahedral
       points) are not constrained.

       More Hessian: Some experimental stuff using the Hessian matrix can be
       accessed with the command "hessian_menu".  This brings up a menu of
       various things.  Some of the more interesting: choice E will find the
       lowest eigenvalue and corresponding eigenvector.  Useful at a saddle
       point.  After E, use choice S to move along eigenvector direction to minimum
       energy.  Choice P finds the number of eigenvalues above and below
       a value.

       The command "saddle" will seek lowest energy along the lowest eigenvalue's
       eigenvector, without the need to go into hessian_menu.

       Conjugate gradient now does the Polak-Ribiere variety of the algorithm as
       the default.  Seems to work much better than the previous Fletcher-Reeves
       variety, especially in automatically restarting itself when it gets in
       trouble.

       Users can send geomview commands through Evolver.  Syntax:
       geomview "command"
       Example:
       geomview "(transform mound mound Camera rotate 1 0 0)"
       Useful in scripts to have geomview save frames for a movie.

       The gravity-setting 'G' command now takes a numerical argument instead of
       a repetition count.  So "G 5" sets gravity to 5 instead of producing 5
       gravity prompts.

       The name of the current datafile can be referred to in commands as
       `datafilename' wherever a string can be used.  See next item.

       sprintf, printf now accept string arguments, but a string pointer is pushed
       as 8 bytes on the calling stack to C's sprintf, so %s in format string should
       be followed by %0.0s to dispose of the second half.  Example:
       printf "This is %s%0.0s with total energy %f\n",datafilename,total_energy

       The print command also accepts strings. Example: print datafilename

       'Extra' attributes now inherited for same type element.  That is, edges
       formed from subdividing an edge will inherit its extra attributes.

       Added 'jiggle' toggle command, and jiggle_temperature internal variable.

       Added total_time internal variable. Settable also.

    End of newsletter 9.

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