File: single.htm

package info (click to toggle)
evolver 2.30c-2
links: PTS
area: main
in suites: squeeze
size: 11,204 kB
ctags: 10,247
sloc: ansic: 118,999; makefile: 98
file content (704 lines) | stat: -rw-r--r-- 32,514 bytes
parent folder | download | duplicates (3)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HEAD><TITLE>Surface Evolver Documentation: single letter main commands
</title></head>

<BODY>
<center>
<h1><a href="http://www.susqu.edu/facstaff/b/brakke/evolver/evolver.htm">
Surface Evolver</a> Documentation</h1>
</center>
<a href="evolver.htm#doc top">Back to top of Surface Evolver documentation.</a>
<a href="index.htm">Index.</a>

<hr><a name="single letter"> </a>
<h2>Single letter main commands</h2>

The oldest and most commonly used Surface Evolver
 commands are just single letters.
Case is significant for these. Single letters are always interpreted
as commands, so you may not use single letters for variable names. 
Single letter commands may be <a href="#redefinition">redefined</a>.<p>

Single letter commands may be summarized in five groups:
<ul><li>             Reporting:
<ul>  <li><a href="#C"> C</a> Run consistency checks.
  <li><a href="#c"> c</a> Report count of elements.
  <li><a href="#e"> e</a> Extrapolate.
  <li><a href="#i"> i</a> Information on status.
  <li><a href="#v"> v</a> Report volumes.
  <li><a href="#X"> v</a> List extra attributes.
  <li><a href="#z"> z</a> Do curvature test.
</ul><li>             Model characteristics: 
<ul>  <li><a href="#A"> A</a> Display and set variables and various parameters.
  <li><a href="#a"> a</a> Toggle area normalization
  <li><a href="#b"> b</a> Set body pressures.
  <li><a href="#f"> f</a> Set diffusion constant.
  <li><a href="#G"> G</a> Set gravity.
  <li><a href="#J"> J</a> Toggle jiggling on every move.
  <li><a href="#k"> k</a> Set boundary gap constant.
  <li><a href="#M"> M</a> Toggle linear/quadratic model.
  <li><a href="#m"> m</a> Toggle fixed motion scale.
  <li><a href="#p"> p</a> Set ambient pressure.
  <li><a href="#Q"> Q</a> Report or set quantities.
 <li><a href="#U"> U</a>  Toggle conjugate gradient method.
  <li><a href="#W"> W</a> Homothety toggle.
</ul><li>               Surface modification
<ul>  <li><a href="#g"> g</a> Go one iteration step. Often followed by a repetition count.
  <li><a href="#j"> j</a> Jiggle once.
  <li><a href="#K"> K</a> Skinny triangle long edge divide.
  <li><a href="#l"> l</a> Subdivide long edges.
  <li><a href="#N"> N</a> Set target volumes to actual.
  <li><a href="#n"> n</a> Notch ridges and valleys.
  <li><a href="#O"> O</a> Pop non-minimal edges.
  <li><a href="#o"> o</a> Pop non-minimal vertices.
  <li><a href="#r"> r</a> Refine triangulation.
  <li><a href="#t"> t</a> Remove tiny edges.
  <li><a href="#u"> u</a> Equiangulate.
  <li><a href="#V"> V</a> Vertex averaging.
  <li><a href="#w"> w</a> Weed out small triangles.
  <li><a href="#y"> y</a> Torus duplication.
  <li><a href="#Z"> Z</a> Zoom in on vertex.
</ul><li>            Output: 
<ul><li><a href="#D"> D</a>  Toggle display every iteration.
  <li><a href="#d"> d</a> Dump surface to datafile.
  <li><a href="#P"> P</a> Graphics output (geomview, Postscript, etc.).
  <li><a href="#s"> s</a> Screen display (native graphics).
</ul><li>               Miscellaneous: 
<ul>  <li><a href="#F"> F</a>  Toggle command logging.
  <li><a href="#H"> H,h,?</a> Help screen.
  <li><a href="#q"> q,x</a>   Exit.
</ul></ul><P>

<hr><a name="redefinition"></a><h2>Single letter redefinition</h2>
It is possible to reassign a single letter to your own command
by the syntax
<pre> <i>letter</i> :::= <i>command</i>
</pre>
but this should only be used in special circumstances, such as
redefining  'r' to do additional actions along with refinement.
The standard meaning can be restored with a null assignment:
<pre> <i>letter</i> :::=
</pre>
Use single quotes around the letter to get the standard meaning, i.e. 'r'
will do a standard refine when r has been redefined.
Redefinitions are cleared when a new surface is loaded.  Be careful
when using redefined commands in defining other commands.
Redefinition is effective on execution of the redefinition command,
not on parsing. Redefinition is not retroactive to uses in previously
defined commands, but restoring the standard meaning is retroactive.
Examples:
<pre>
   V :::= { fix vertex[5]; 'V'; unfix vertex[5] }
   r :::= { divisions := divisions * 2; 
            hooke_length := hooke_length/2; 'r' }
</pre>
<hr><a name="A"> </a>
<h2>A</h2>
<a href="#single letter">Single letter</a> main command.
  Lists the current values of 
<a href="syntax.htm#variables">variables</a> and 
<a href="quants.htm#named quantities">named quantity</a> values, moduli,
and targets.  Only explicitly user-defined named quantities are
shown unless <a href="toggle.htm#show_all_quantities">
show_all_quantities</a> is toggled on.
  You are allowed you to enter new values (except quantity values). 
 The new value is entered as the
  number of the variable (from the list) and the new value.  
   Exit by hitting RETURN on a blank line.  All changes that
  can be made here can also be made with 
  <a href="commands.htm#assignment">assignment</a>
  commands.

<hr><a name="a"> </a>
<h2>a</h2>
<a href="#single letter">Single letter</a> main command.
  Toggles <a href="model.htm#area normalization">area normalization</a>
   of vertex forces and other gradients, to model motion by mean
   curvature.  Meant to be used with a fixed 
   <a href="iterate.htm#scale factor">scale factor</a>.
    Be sure you have a small enough scale factor or else things tend to
  blow up.  Reduce the scale factor temporarily after refinement, since
  triangle areas are cut by a factor of 4 but the old creases remain. 
  When this option is ON, there is an optional check that can be made
  for facets that move too much.  This is done by computing the ratio
  of the length of the normal change to the length of the old normal. 
  If this exceeds the user-specified value, then all vertices are
  restored to their previous position.  The user should reduce the
  motion scale factor and iterate again.<P>

<hr><a name="b"> </a>
<h2>b</h2>
<a href="#single letter">Single letter</a> main command.
 Permits user to interactively change body 
 <a href="elements.htm#target volume">prescribed volumes</a> or
 <a href="elements.htm#body pressure">pressures</a>.  
 Prints old value for each body and prompts for new.  <P>

<hr><a name="C"> </a>
<a name="check"></a>
<h2>C</h2>
<a href="#single letter">Single letter</a> main command.
 Runs various internal consistency checks. Synonym: check.
 If no problems, just prints "Checks completed."
 The number of errors found is stored in the variable check_count.
 The checks are: <ul>
 <li>  Element list integrity - checks that
       data structures are intact.
 <li>  Facet-edge check - that if a facet adjoins
       an edge, then the edge adjoins the facet,
       and that the three edges around a facet
       link up.
 <li>  Facet-body check - whether adjacent facets
       have the same body on the same side.
 <li>  Collapsed elements - check if endpoints of
       an edge are the same, and whether
       neighboring facets share more than one
       edge and two vertices.
</ul>

<hr><a name="c"> </a> <a name="counts"></a>
<h2>c</h2>
<a href="#single letter">Single letter</a> main command.
 Prints count of elements and memory used.
 The memory is just the total of the element structures.
 On some systems, enabling "<a href="toggle.htm#memdebug">memdebug</a>" 
 will print more
 complete statistics on total memory usage.  Synonym: counts.

<hr><a name="D"> </a>
<h2>D</h2>
<a href="#single letter">Single letter</a> main command.
   Toggles updating graphics every iteration or other surface change.  
    Default is to display.  Status can also be changed or 
    queried with the <a href="toggle.htm#autodisplay">autodisplay</a>
    toggle.

<hr><a name="d"> </a>
<h2>d</h2>
<a href="#single letter">Single letter</a> main command.
 Dumps data to ASCII file in same format as initial data file.  You
 will be prompted for a filename.  An empty reponse will use the
 default dump name, which is the datafile name with a ".dmp"
 extension.  Same as the <a href="commands.htm#dump">dump</a>
 command, except the dump command requires the filename as part
 of the command.  Useful for checking your input is being read correctly,
 for saving current configuration, and for debugging.<P>

<hr><a name="e"> </a> <a name="extrapolate"></a>
<h2>e</h2>
<a href="#single letter">Single letter</a> main command.
   Extrapolates total energy to infinite refinement if at least two
   <a href="single.htm#r">r</a> commands have been done.  
   Uses last energy values at three
   successive levels of refinement, and uses a power law fit for the
   error.  For best results, use only the
   r command to refine, and iterate to complete convergence at each
   level of refinement. Synonym: extrapolate.

<hr><a name="F"> </a>
<h2>F</h2>
<a href="#single letter">Single letter</a> main command.
 Toggle logging of commands in file.  If starting logging, you will be
 prompted for the name of a log file.  Any existing file of that name
 will be appended to.  Logging stops automatically when the surface is
 exited.  Only correctly parsed commands are logged.  Output resulting
from commands is not logged.  Responses to interactive single-letter
commands are logged, but not responses to other interactive commands.


<hr><a name="f"> </a>
<h2>f</h2>
<a href="#single letter">Single letter</a> main command.
Sets <a href="iterate.htm#diffusion">diffusion constant</a>.  
Prints old and prompts for new.<P>

<hr><a name="G"> </a>
<h2>G</h2>
<a href="#single letter">Single letter</a> main command.
 Toggles <a href="energies.htm#gravity energy">gravity</a>
 on or off.  Gravity starts ON if any body has a
 nonzero density; otherwise OFF.  If followed by a value, sets gravity
 to that value.  Otherwise prints old value of gravitational constant
 and prompts for new.  

<hr><a name="go"></a>
<a name="g"> </a>
<h2>g</h2>
<a href="#single letter">Single letter</a> main command.
 Do one <a href="iterate.htm#iteration step">iteration step</a>.  
 The output consists of the number of iterations left (for people who
 wonder how close their 1000 iterations are to ending), the area and
 energy, and the <a href="iterate.htm#scale factor">scale factor</a>.  
<tt>g</tt> is commonly used with an iteration count, as in "<tt>g 100</tt>".
The user can abort repeated iterations
 by sending an interrupt to the process (SIGINT, to be precise; CTRL-C
 or whatever on your keyboard).  As a special dispensation to lazy users,
the syntax "<tt>g</tt><i>n</i>" is equivalent to "<tt>g</tt> <i>n</i>".
Synonym: go

<hr><a name="H"> </a>
<h2>H,h,?</h2>
<a href="#single letter">Single letter</a> main command.
 Prints a very primitive help message listing common commands.
 <a href="commands.htm#help">help</a> is much better, as it
 accesses the full HTML documentation.  Or best, use a separate
 HTML browser on this documentation.<P>

<hr><a name="i"> </a>
<h2>i</h2>
<a href="#single letter">Single letter</a> main command.
  Prints miscellaneous information:
<ul>
<li>  Name of datafile
<li>  Total energy
<li>  Total area of facets
<li>  Count of elements and memory usage
<li>  Area normalization, if on
<li>  LINEAR or QUADRATIC model
<li>  Whether conjugate gradient on
<li>  Order of numerical integration
<li>  Scale factor value and option (fixed or optimizing)
<li>  Diffusion option and diffusion constant value
<li>  Gravity option and gravitational constant value
<li>  Jiggling status and temperature
<li>  Gap constant (for gap energy, if active)
<li>  Ambient pressure (if ideal gas model in effect)
</ul><P>

<hr><a name="J"> </a>
<h2>J</h2>
<a href="#single letter">Single letter</a> main command.
 Toggles <a href="#j">jiggling</a>
 on every iteration of the <a href="single.htm#g">g</a>
 command.  If jiggling gets turned on,
 prompts for temperature value.
Default temperature is the value of the 
<a href="syntax.htm#jiggle_temperature">temperature</a> internal variable.<P>

<hr><a name="j"> </a>
<h2>j</h2>
<a href="#single letter">Single letter</a> main command.
 Jiggles all vertices once.  Meant to be used for simulated annealing.
 Useful for shaking up surfaces that get in
 a rut, especially crystalline integrands.  You will be prompted for a
 "temperature" which is used as a scaling factor, if you don't give a
 temperature with the command.  
Default temperature is the value of the 
<a href="syntax.htm#jiggle_temperature">jiggle_temperature</a>
 internal variable, which starts as 0.05.
The actual jiggle is a random
 displacement of each vertex independently with a Gaussian
 distribution with deviation being the temperature times the mean
 edge length.  See the 
<a href="commands.htm#longj">longj</a> command for a user-definable
 perturbation.  <P>

<hr><a name="K"> </a>
<h2>K</h2>
<a href="#single letter">Single letter</a> main command.
 Finds skinny triangles whose smallest angle is less than a specified
 cutoff.  You will be prompted for a value if you don't give a value
on the command line.  Such triangles will have
 their longest edge subdivided.  Should be followed with tiny edge
 removal (<a href="single.htm#t">t</a>) and equiangulation 
 (<a href="single.htm#u">u</a>).  <P>

<hr><a name="k"> </a>
<h2>k</h2>
<a href="#single letter">Single letter</a> main command.
 Sets "gap constant" for <a href="energies.htm#gap energy">gap energy</a>
 for <a href="constrnt.htm#convex constraint">convex constraints</a>.  Adds
 energy roughly proportional to area between edge and boundary.  You
 will be prompted for a value if you don't give a value
on the command line.  Normal values are on the order of
 magnitude of unity.  Value k = 1 is closest to true area.  Use 0 to
 eliminate the energy.  <P>

<hr><a name="l"> </a>
<a name="edge_divide"></a>
<h2>l  (lower case L)</h2>
<a href="#single letter">Single letter</a> main command.
 Subdivides long edges, creating new facets as necessary.  You will be
 prompted for a cutoff edge length, if you don't give a value with the
 command.  Existing edges longer than the cutoff will be divided once
 only.  Newly created edges will not be divided.  Hence there may be
 some long edges left afterward.  If you enter h, you will get a
 histogram of edge lengths.  If you hit RETURN with no value, nothing
 will be done.  It is much better to use the refine command
<a href="single.htm#r">r</a>  than to subdivide all
 edges.  A synonym for "<tt>l</tt> <i>value</i>" is "<tt>edge_divide</tt> <i>value</i>".  This command does not respect the <a href="elements.htm#no_refine">
no_refine</a> attribute.
 <P>

<hr><a name="M"> </a>
<h2>M</h2>
<a href="#single letter">Single letter</a> main command.
 Sets model type to 
 <a href="model.htm#linear model">linear</a> , 
 <a href="model.htm#quadratic model">quadratic</a>, or
<a href="model.htm#Lagrange model">Lagrange</a>.  Changing from LINEAR to
 QUADRATIC adds vertices at the midpoints of each edge.  Changing from
 QUADRATIC to LINEAR deletes the midpoints.  Optionally takes new model
 type ( 1 for LINEAR,  2 for QUADRATIC, &gt; 2 for Lagrange.  )
 on command line.  Otherwise will prompt you.<P>

<hr><a name="m"> </a>
<h2>m</h2>
<a href="#single letter">Single letter</a> main command.
 Toggles quadratic search for  
<a href="iterate.htm#optimizing scale">optimal</a> global motion 
 <a href="#g">scale factor</a>.  If
 search is toggled OFF, you will be prompted for a fixed scale factor.  If
 you give a value with the command, then you are setting a fixed scale
 factor.


<hr><a name="N"> </a>
<h2>N</h2>
<a href="#single letter">Single letter</a> main command.
 Set body <a href="elements.htm#target volume">target volumes</a>
 to current actual <a href="elements.htm#body volume">volumes</a>.  <P>

<hr><a name="n"> </a>
<h2>n</h2>
<a href="#single letter">Single letter</a> main command.
  Notching ridges and valleys.  Finds edges that have two adjacent
  facets, and those facets' normals make an angle greater than some
  cutoff angle.  You will be prompted for the cutoff angle (radians) if
  you don't give a value with the command.  Qualifying edges will have
  the adjacent facets subdivided by putting a new vertex in the center. 
  Should follow with 
<a href="#u">equiangulation</a>.  In the 
<a href="model.htm#string model">string model</a>, it will
  refine edges next to vertices with angle between edges (parallel
  orientation) exceeding the given value.  Optionally takes cutoff
  angle on command line.  <P>

<hr><a name="O"> </a>
<h2>O</h2>
<a href="#single letter">Single letter</a> main command.
 
  Pop non-minimal edges.  Scans for edges with more than three facets
  attached.  Splits such edges into triple-facet edges.  Splits
  propagate along a multiple edge until they run into some obstacle. 
  This command is meant for surfaces that have equal tension on all
  facets.  Also tries to pop edges on walls properly.  For finer
  control on which edges to try, use the <a href="commands.htm#pop">pop</a>
  command.
  Try octa.fe for an example.  <P>

<hr><a name="o"> </a>
<h2>o</h2>
<a href="#single letter">Single letter</a> main command.
 Pop non-minimal vertices.  This command scans the surface for vertices
 that don't have the topologies of one of the three minimal tangent
 cones that are legal in soap films (plane, triple edge, tetrahedral point).
  These are "popped" to proper local topologies.  
The algorithm is to replace the vertex with a sphere.  The facets into the
original vertex are truncated at the sphere surface.  The sphere is divided
into cells by those facets, and the largest cell is deleted, which preserves
the topology of the complement of the surface.
A special case is two cones meeting at a vertex; if the cones are broad
enough, they will be merged, otherwise they will be split.  In case of
merging cones, if both cone interiors are defined to be part of the same
body, then no facet is placed across the neck created by the merger; if they
are different bodies or no bodies, a facet will be placed across the neck.
Only vertices in the interior of a surface, not
 fixed or on constraints or boundaries, are tested.
   Try popstr.fe and octa.fe
 for examples.<P>

<hr><a name="P"> </a>
<h2>P</h2>
<a href="#single letter">Single letter</a> main command.
 Produce graphics output files.  "P" is for "picture".
  This brings up a menu, unless you give the menu option on the command line.
 For the 2D graphics options, the view is the same as seen with the 
<a href="#s">s</a> command. 
 For options that output to a file, you will be prompted for a filename.
 Some other possible options you may be asked:
<dl>
<dt><tt>Display raw cells, connected bodies or clipped cells? (0,1,2)</tt></dt>
<dd>  If you are doing <a href="model.htm#torus model">torus model</a>,
 you will be asked for a <a href="model.htm#torus display">display option</a>,
unless you have already set one. </dd>
<dt><tt>Do normal interpolation?</tt></dt>
<dd>
  Some formats are capable of doing
interpolation between vertex normals for smoother shading, and you will
be asked if you want to do that.</dd>
<dt><tt>Do inner, outer, or all surfaces? (i,o,a)</tt></dt>
<dd> When bodies are present, there is an
option to plot the inner surfaces(adjacent to two bodies), outer surfaces
(adjacent to 0 or 1 bodies), or all surfaces
of the bodies.</dd>
<dt><tt>Do body colors?</tt> </dt>
<dd> This gives you a chance to
color the bodies differently.  If you do, the current colormap
file will be used to color the bodies according to id number.
  This scheme is a relict
of early days of the Evolver, and it is suggested that you use the
<a href="elements.htm#facet color">color</a>, 
<a href="elements.htm#frontcolor">frontcolor</a>
 and <a href="elements.htm#backcolor">backcolor</a> facet attributes instead. </dd>
<dt><tt>Enter name of colormap file: </tt></dt>
<dd>  If there is no
current colormap file, you will be prompted. 
 The colormap file has the format of
 RGB values, one set per line, values between 0 and 1.  (This map may
 not be effective on all devices.)</dd>
<dt><tt> Thicken? (n | y [thickness(0.001)])</tt></dt>
<dd>
 You may also be asked if you want thickening.  If you do, each facet
 will be recorded twice, with opposite orientations, with vertices
 moved from their original positions by the thickening distance (which
 the option lets you enter) in the normal direction.  The normal used
 at each vertex is the same as used for normal interpolation, so all
 the facets around a planar vertex will have that vertex moved the same
 amount.  Triple junctions will be separated.  Thickening is good for
 rendering programs that insist on consistently oriented surfaces, or
 that have problems with show-through of
 the backside of a surface.
 Choosing 'y' or 'n'
will  reset the thicken toggle.  If you answer 'y', you can optionally
specify the thickness, which defaults to the value of the 
<a href="syntax.htm#thickness">thickness</a> internal variable.</dd>

</dl>
The menu choices for types of output are:
<dl>
<dt><tt>1. Pixar file</tt></dt>
<dd>  For Pixar format.  Actually same format as option 2.</dd>
<dt><tt>2. OOGL file</tt></dt>
<dd>This is a file in a file format used by
<a href="graphics.htm#geomview">geomview</a>, which is Object Oriented
Graphics Language.  Suitable for direct input into geomview.</dd>
<dt><tt>3. PostScript file</tt></dt>
<dd> Generates a <a href="graphics.htm#postscript">PostScript file</a>.</dd>
<dt><tt>4. Triangle file</tt></dt>
<dd>A private format file, just listing data.  Not much use any more.</dd>
<dt><tt>5. Softimage file</tt></dt>
<dd>Output file in Softimage format.</dd>
<dt><tt>8. Start simultaneous geomview</tt></dt>
<dd>If you have the <a href="graphics.htm#geomview">geomview</a> package installed,
this command will start geomview and display the current surface.
Changes to the surface are automatically displayed unless
<a href="toggle.htm#autodisplay">autodisplay</a> is toggled off.</dd>
<dt><tt>9. End simultaneous geomview</tt></dt>
<dd>Terminates any <a href="graphics.htm#geomview">geomview</a> program or
pipe.</dd>
<dt><tt>A. Start OOGL pipe.</tt></dt>
<dd> Geomview uses a pipe interface at the moment.  
 This starts a named pipe with geomview output, but
 without invoking geomview.  You will be told the
 name of the pipe, and it is up to you to start a pipe reader.  Evolver
 blocks until a pipe reader is started.  This is useful for having a
 second instance of Evolver feed a second surface to geomview by having
 geomview load the pipe.  Also good for checking exactly what Evolver
is sending to geomview.  The <a href="commands.htm#geompipe">geompipe</a>
command does the same thing.  Terminate the pipe with "P 9".
Note that only one geomview output at a time is possible, so you
can't have a geomview display and separate pipe active at the same time.</dd>
<dt><tt>B. End OOGL pipe.</tt></dt>
<dd>Same as option 9.</dd>
</dl>
<hr><a name="p"> </a>
<h2>p</h2>
<a href="#single letter">Single letter</a> main command.
 Sets ambient pressure in 
<a href="datafile.htm#ideal gas decl">ideal gas model</a>. 
If you don't give a value
 with the command, you will be prompted. A large value gives more
 incompressible bodies.<P>

<hr><a name="Q"> </a>
<h2>Q</h2>
<a href="#single letter">Single letter</a> main command.
Report current values of user-defined
method instances and named quantities.  If the show_all_quantities toggle
is on, then internal quantities and method instances are also shown.
This is particularly informative if convert_to_quantities has been done
(same as -q command line option), since then internal values such as
constraint integrals are in the form of method instances.
  <P>

<hr><a name="q"> </a>
<h2>q</h2>
<a href="#single letter">Single letter</a> main command.
 Exit program.  You will be given a chance to have second thoughts. 
 You may also load a new datafile.  Automatically closes graphics if
 you really quit.  Does not save anything.  <P>

<hr><a name="r"> </a>
<h2>r</h2>
<a href="#single letter">Single letter</a> main command.
 Refines the triangulation.  Edges are divided in two, and facets are
 divided into four facets with inherited attributes. 
Edges and facets with the no_refine attribute set are not refined.
  Reports the
 number of element structures and amount of memory used by those structures.  <P>

<hr><a name="s"> </a>
<h2>s</h2>
<a href="#single letter">Single letter</a> main command.
 Shows the surface with <a href="graphics.htm#screen graphics">screen
 graphics</a>. Goes into the
 graphics command mode.  <a href="model.htm#torus model">Torus model</a>
 surfaces have 
<a href="model.htm#torus display">display options</a>
 you will be asked for the first time.
  The graphics window may be closed with the 
<a href="commands.htm#close_show">close_show</a>
 command.<P>

<hr><a name="t"> </a>
<h2>t</h2>
<a href="#single letter">Single letter</a> main command.
  Eliminates tiny edges and their adjacent facets.  You will be
  prompted for a cutoff edge length if you don't give a value with the
  command.  If you enter h, you will get an edge length histogram.  If
  you hit RETURN without a value, nothing will happen.  Some edges may
  not be eliminable due to being FIXED or endpoints having different
  attrtibutes from the edge.<P>

<hr><a name="U"> </a>
<h2>U</h2>
<a href="#single letter">Single letter</a> main command.
  This toggles 
<a href="iterate.htm#conjugate gradient">conjugate gradient</a>
 mode, which will usually give faster
  convergence to the minimum energy than the default gradient descent
  mode.  The only difference is that motion is along the conjugate
  gradient direction.  The 
<a href="iterate.htm#scale factor">scale factor</a>
 should be in optimizing mode. 
  The conjugate gradient 
history vector is reset after every surface modification, such as
  refinement or equiangulation.  After large changes (say, to volume),
  run without conjugate gradient a few steps to restore sanity.<P>

<hr><a name="u"> </a>
<a name="equiangulation"></a>
<h2>u</h2>
<a href="#single letter">Single letter</a> main command.
  This command, called "equiangulation", tries to polish up the
  triangulation.  In the <a href="model.htm#soapfilm model">
  soapfilm model</a>, each edge that has two neighboring facets (and hence
  is the diagonal of a quadrilateral) is tested to see if switching the
  quadrilateral diagonal would make the triangles more equiangular. 
  For a plane triangulation, a fully equiangulated triangulation is a
  Delaunay triangulation, but the test makes sense for skew
  quadrilaterals in 3-space also.  It may be necessary to repeat the
  command several times to get complete equiangulation.  The 
  <a href="commands.htm#edgeswap">edgeswap</a>
   command can force flipping of prescribed edges.<P>
   In the <a href="model.htm#simplex model">simplex model</a>,
   equiangulation works only for surface dimension 3.  There, two
   types of move are available when a face of a tetrahedron violates
   the Delaunay void condition: replacing two tetrahedra with a common
   face by three, or the reverse operation of 
   replacing three tetrahedra around a common edge by two, 
   depending on how the condition is violated.
  This command is inoperative in the string model.
<hr><a name="V"> </a>
<h2>V</h2>
<a href="#single letter">Single letter</a> main command.
 Vertex averaging.  For each vertex, computes new position as
 area-weighted average of centroids of adjacent facets.  Only adjacent
 facets with the same constraints and boundaries are used.  Preserves
 volumes, at least to first order.  See the 
 <a href="commands.htm#rawv">rawv</a> command for vertex
 averaging without volume preservation, and 
 <a href="commands.htm#rawestv">rawestv</a> for ignoring
 likeness of constraints.  Vertices on triple edges are averaged
 only with adjacent vertices on the triple edge, and then only if 
there are exactly two neighboring triple edge vertices. 
 Fixed vertices do not move. 
 Vertices on constraints are projected back onto their
 constraints.  The computation of new vertex positions are all
done before any vertex is moved.  For sequential movement
applied to a subset of vertices, see the
<a href="commands.htm#vertex_average">vertex_average</a> command.<P>

<hr><a name="v"></a>
<a name="show_vol"></a>
<h2>v</h2>
<a href="#single letter">Single letter</a> main command.
 Shows target volume, actual volume, and pressure of each body. 
 Also shows named quantities.  Pressures are really the Lagrange
 multipliers.  Pressures are computed before an iteration, so the
 reported values are essentially are one iteration behind.
 Synonym: show_vol <P>

<hr><a name="W"> </a>
<h2>W</h2>
<a href="#single letter">Single letter</a> main command.
  Toggles homothety.  If homothety ON, then after every iteration, the
  surface is scaled up so that the total volume of all bodies is 1. 
  Meant to be used on surfaces without any blowup constraints of any
  kind, to see the limiting shape as surface collapses to a point.  <P>

<hr><a name="w"> </a>
<h2>w</h2>
<a href="#single letter">Single letter</a> main command.
 Tries to weed out small triangles.  You will be prompted for the
 cutoff area value if you don't give a value with the command.  If you
 enter h, you will get a histogram of areas to guide you.  If you hit
 RETURN with no value, nothing will be done.  Some small triangles may
 not be eliminable due to constraints or other such obstacles.  The
 action is to eliminate an edge on the triangle, eliminating several
 facets in the process.  Edges will be tried for elimination in
 shortest to longest order.  WARNING: Although checks are made to see
 if it is reasonable to eliminate an edge, it is predicated on facets
 being relatively small.  If you tell it to eliminate all below area 5,
 Evolver may eliminate your entire surface without compunction.<P>

<hr><a name="X"> </a>
<h2>X</h2>
<a href="#single letter">Single letter</a> main command.
List the current <a href="elements.htm#extra attributes">extra attributes</a>,
including name, dimension, type, size in bytes, and offset within the
element structure.  Some internal attributes are also listed, whose names
begin with a double underscore.

<hr><a name="x"> </a>
<h2>x</h2>
<a href="#single letter">Single letter</a> main command.
Same as q.   Exit Evolver, or start new surface. <P>

<hr><a name="y"> </a>
<h2>y</h2>
<a href="#single letter">Single letter</a> main command.
 Torus duplication.  In 
<a href="model.htm#torus model">torus model</a>,
 prompts for a period number (1,2,
 or 3) and then doubles the torus unit cell in that direction.  Useful
 for extending simple configurations into more extensive ones.<P>

<hr><a name="Z"> </a>
<h2>Z</h2>
<a href="#single letter">Single letter</a> main command.
  Zooms in on a vertex.  Asks for vertex number and radius.  Number is
  as given in vertex list in datafile.  Beware that vertex numbers
  change in a dump (but correct current zoom vertex number will be
  recorded in dump).  Eliminates all elements outside radius distance
  from vertex 1.  New edges at the radius are made FIXED.  Meant to
  investigate tangent cones and intricate behavior, for example, where
  wire goes through surface in the overhand knot surface.  Zooming is
  only implemented for surfaces without bodies.  <P>

<hr><a name="z"> </a>
<h2>z</h2>
<a href="#single letter">Single letter</a> main command.
 Do curvature test on QUADRATIC model.  Supposed to be useful if you're
 seeking a surface with monotone mean curvature.  Currently checks
 angle of creases along edges and samples curvature on facet interiors. 
 Orientation is with respect the way facets were originally defined.
 Deprecated.<P>

<hr>
<a href="evolver.htm#doc top">Back to top of Surface Evolver documentation.</a>
<a href="index.htm">Index.</a>
</body>
</html>