# Surface Evolver Newsletter no. 10

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                          Surface Evolver Newsletter Number 10
                                  December 16, 1994

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

    Contents:
      Query on curvature.
      Version 1.97

    Query on curvature.
      From Christian Burger <burger@pc1442.phys-chemie.uni-marburg.de>:

         I am interested in the investigation of physical systems which are
         usually highly symmetric two-phase systems separated by an interface
         which should be some kind of minimal surface. Very often, the systems
         are bicontinuous, i.e., two unconnected 3D network domains live in a
         common matrix of surrounding matter (I'm speaking in physical terms
         here, not mathematical). Naturally, I'm using the evolver with the
         torus model. The domains have defined volumes and are incompressible.
         Physical examples for such systems are micro-emulsions,
         polyelectrolyte-surfactant complexes, block copolymers, etc. It is
         likely that curvature plays an important role for these systems. If the
         structure unit building up the interface is not symmetric this leads to
         a `spontaneous curvature', i.e., a finite H_ZERO in terms of evolver
         nomenclature.  If you are aware of any work in this direction people
         have done so far using the evolver, I'd like to get some references on it.

    Version 1.97:

     Version 1.97 is now available for ftp (except Mac version hasn't
     been updated yet.)

     Changes from 1.96 are mostly a lot of obscure bug fixes.  But
     there are some new features of general interest.

     New Hessian commands: "eigenprobe value" will print the number of
     eigenvalues of the energy Hessian that are less than, equal to, and
     greater than the given value.  It is OK to use an exact eigenvalue
     (like 0, often) for the value.   Useful for probing stability.
     "lanczos value" will do a little Lanczos algorithm and report
     the 15 nearest approximate eigenvalues to the given value.  Do not
     use an eigenvalue for the value! Not real polished yet.

     The default way of factoring the Hessian is with routines from the
     Yale Sparse Matrix Package (YSMP), patched a bit to cope with zeroes
     on the diagonal.  I've been tinkering around with my own version
     of minimal degree factoring that is a little more aware of the
     surface structure.  It can be activated by "ysmp off" and deactivated
     by "ysmp on".  My version seems to have 10-20% less fill, and so
     be a little faster.  It also seems to not have as many spurious
     zeroes on the diagonal.  Further, in an attempt to cope with
     indefinite Hessians, there is a toggle "bunch_kauffman" that enables
     a version of Bunch-Kauffman factoring in my version.

     Certain named quantity attributes can now be referred to in expressions.
     For quantity qqq, qqq.value is the current value, qqq.target is
     the constrained value, qqq.modulus is the same as the modulus in the
     datafile definition, and qqq.pressure is the Lagrange multiplier
     for a constrained quantity.  You can assign values to qqq.modulus
     and qqq.target.

     The dump command 'd' now saves almost all toggle states (except some
     debugging toggles) if not the default values.

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