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Index.
Surface Evolver syntax
Both the datafile and user commands follow a common general syntax
described in this file, with a few differences as noted.
Lexical format
For those who know about such things,
the datafile and commands are read with a lexical analyzer generated
by the lex program. The specification is in datafile.lex. Commands
are further parsed by a yaccgenerated parser.
In parsing an expression, the longest legal expression
is used. This permits coordinates to be specified by
several consecutive expressions with no special
separators.
Comments
Comments may be enclosed in /* */ pairs (as in C) and
may span lines. // indicates the rest of the line is a comment,
as in C++.
Lines and line splicing
The file is made up of lines. Line breaks are significant.
The next physical line can be spliced onto the current
line by having \ be the last character of the current line.
Line splicing is not effective in // comments.
Blank lines and comment lines may be placed freely anywhere.
The various combinations of CR and NL that
various computer systems use are all recognized
Case
Upper and lower case is not significant in the datafile, except in
#define macro names. In runtime commands, case is only
significant
for singleletter commands.
Whitespace
In the datafile, whitespace consists of spaces, tabs, commas, colons,
and semicolons. So it's fine if you want to use commas to
separate coordinate values, and colons to prettify constraint
definitions. In commands, whitespace consists of spaces and tabs.
CTRLZ is also whitespace, for the benefit of files imported from
DOS.
Identifiers
Identifiers follow standard
C rules (composed of alphanumeric characters and '_'
with the leading character not a digit) and must not
be keywords. Identifiers are used for macro names
(in the datafile) and userdefined
variables and
commands.
Identifiers must have at least two characters,
since single characters can be confused with commands.
To find out if a name is already in use as a keyword or
userdefined name interactively, use
help command. In scripts, one
can use the is_defined function, which has the syntax
is_defined(stringexpr)
The stringexpr must be a quoted string or other string expression.
The return value is 0 if the name is undefined, 1 if defined.
This function is evaluated at runtime, but variables in the whole
command are parsed before the command is executed, so a command
like if is_defined("newvar") then newvar := 1 else newvar := 2
will give newvar
the value 1 even if this is its first appearance.
A better way in scripts to test is to use the define
command to define the variable without initialization, and then test to
see if it has the default value, i.e. 0 for a numeric variable and a
sizeof 0 for a string variable.
Numbers
Constant values may be in any of the usual forms. This
includes integers, fixed point, and scientific notation
such as
2 3 .5 23. 5e10 +0.7D2
Hexadecimal integers starting with 0x, as in 0x12Af, are also accepted,
as are binary numbers such as 11001b, indicated by a trailing 'b'.
Color names are interpreted as integers.
Colors
The colors of edges
and facets
are recorded as integers in the
range 1 through 15. How these
integers translate to colors on the screen is determined by how
Evolver's graphics drivers are written. The following synonyms are
supplied, and it is hoped that the
graphics drivers will be written to display these correctly:
1 CLEAR
0 BLACK
1 BLUE
2 GREEN
3 CYAN
4 RED

5 MAGENTA
6 BROWN
7 LIGHTGRAY
8 DARKGRAY
9 LIGHTBLUE
10 LIGHTGREEN

11 LIGHTCYAN
12 LIGHTRED
13 LIGHTMAGENTA
14 YELLOW
15 WHITE

The special color value CLEAR (1) makes a facet transparent.
"Transparent" is a synonym for clear.
These tokens are simply translated to integer values wherever they
occur, so these are reserved words. Edge and facet colors may be
set in the datafile or by the set command.
Arithmetic expressions
Arithmetic expressions evaluate to real numbers. Boolean expressions
are a subclass, with zero as false and nonzero as true; true results
evaluate as 1. Ordinary algebraic notation is used.
Constant expressions
Constant expressions are evaluated when parsed. They are denoted
by constexpr in various syntax definitions. They occur
mostly in the datafile. Although they may contain variables,
changing the variable value after parsing has no effect.
Variable expressions (denoted by expr
in syntax definitions) are recorded as parse trees and are reevaluated
each time needed.
Atomic values
The following evaluate to single numbers in expressions:
 number
 An integer, real, or hexadecimal constant.
Hex numbers begin with
0x
.
 pi
 Mathematical constant, ratio of circle circumference to radius.
 x1,x2,...; x,y,z,w
 Depending on context, space coordinates, vertex coordinates,
edge vector components, or facet normal components.
 p1,p2,...
 Parameters of vertices on
boundaries.
 G
 Current gravitational constant
for calculating gravitational energy.
 userdefined variables
 Arbitrary variables defined in the datafile or at runtime.
 Indexed array variables.
 Userdefined multidimensional arrays of reals or integers, and some internally defined arrays.
 internal variables
 Special predefined variables.
 element attributes
 Things like vertex coordinates, edge length facet area, colors.
 named quantity attributes
 Including modulus, target, value, pressure.
 method instance attributes
 Including modulus, value.
 toggle name

Any toggle command
name may be used as a Boolean variable in an
expression (full word toggles, not single letters). But beware the
ambiguity in interpreting a toggle as a command or a value.
You may have to force the toggle to be interpreted as a value.
"
ad := autodisplay
" sets ad as a command synonym for
autodisplay, while "ad := (autodisplay)
" records the
current boolean value.
String expressions
A string expression evaluates to a string of characters. At present,
the only ways to produce strings are:
 doublequoted string literals, e.g.
"this is a string"
.
The following standard C escape sequences are recognized:
 \n newline
 \r carriage return
 \t tab
 \b backspace
 \q doublequote mark
 \c the character c elsewise
In DOS, MSWindows, or Windows NT paths, use / as the directory separator,
since \ is an escape character. DOS and Windows have always accepted
/ as a directory separator.
 successive doublequoted strings, which are concatenated into
one string when read.
 string variables, either internal like
datafilename
, or userdefined.
 output from
sprintf
.
Arithmetic operators
These are the arithmetic operators that may appear in
expressions:
 +,,*,/
 Usual real arithmetic; +,,* also work with arrays.
NOTE: A '+' or '' preceded by
whitespace and followed
by a number is taken to be a signed number. Thus
"3  5" and "35" are single expressions, but
"3 5" is not. This is for convenience in separating
multiple expressions listed on the same line for
vertex coordinates, metric components, etc. in the datafile.
 idiv
 Integer divide. Rounds toward zero, then does
integer division. Ex: 7 idiv 2 is 3; 3.5 idiv 2.1 is 1; 3 idiv 2 is 1.
 %, mod
 Real arithmetic modulus, x % y = x  floor(x/y)*y.
 imod
 Integer arithmetic modulus,
x imod y = floor(x)  floor(floor(x)/floor(y))*floor(y).
 =
 NOT an assignment operator. Treated as lowprecedence ''
so levelset constraint formulas like x^2 + y^2  R^2 may be written
naturally as x^2 + y^2 = R^2.
 (,)
 Parentheses for grouping and functional notation.
 ^,**
 Raise to real power.
 ? :
 Conditional expression, as in the C language.
x ? y : z evaluates to y if x is nonzero and to z if x is zero.
 ++,
 Cstyle pre and postincrement and decrement commands. These work only
on single variables and only as standalone commands, as in "for"
loops for example:
for ( inx := 1 ; inx <= 10 ; inx++ )
Boolean operators
Boolean expressions
are a subclass of arithmetic expressions,
with zero as false and nonzero as true; true results
evaluate as 1.
==,>,<,>=,<=,!= 
Numerical or boolean comparison. 
NOT, !  Boolean NOT 
AND, &&  Boolean AND, with shortcircuit evaluation. 
OR,   Boolean OR, with shortcircuit evaluation. 
Operator precedences
Here is the order of operator precedence, listed from high to
low with equal precedence on same line, with associativity.
Operator  Associativity 
^,**  left associative 
unary   right associative 
*,/,%,IMOD,IDIV  left associative 
+,  left associative 
on_boundary
on_constraint
hit_constraint
on_quantity
on_method_instance
 nonassociative 
==,>,<,>=,<=,!=  right associative 
NOT, !  right associative 
AND, &&  left associative 
OR,   left associative 
? :  left associative 
=  left associative 
Math functions
These are the math functions available in expressions. They take
one argument in parentheses, except where noted.

abs(x)
 Absolute value.

sqr(x)
 Square.

sqrt(x)
 Square root. Argument must be nonnegative.

sin(x), cos(x), tan(x)
 Trig functions, argument in radians.

acos(x), asin(x), atan(x)
 Inverse trig functions (acos, asin arguments clamped to [1,1]).
Output in radians.

atan2(y,x)
 Inverse tangent, range pi to pi.

log(x), exp(x)
 Natural log, exponentiation base e.

sinh(x), cosh(x), tanh(x)
 Hyperbolic functions.

asinh(x), acosh(x), atanh(x)
 Inverse hyperbolic functions.

pow(x,y)
 Raise x to real power y; x may be negative if y is an integer.

ceil(x), floor(x)
 Round up or down to integer.

minimum(a,b), maximum(a,b)
 Extreme of two arguments.

ellipticE(x), ellipticK(x)
 Complete elliptic functions.

incompleteEllipticE(phi,m), incompleteEllipticF(phi,m)
 Incomplete elliptic functions
of parameters (phi,m); agrees with Mathematica definition.

matrix_multiply(A,B,C)

Builtin matrix multiplication of arrays. Stores A*B in C. A, B, and
C must be standalone 1 or 2 dimensional array variables with appropriately
matching dimensions; in particular, you cannot get a scalar product of
vectors with this, unless you declare A to be 1xN, B to be Nx1, and C to
be 1x1. C must be different from A and B. Does not return a value.
Also doesn't work with array attributes yet. Obsolete, since the * operator
now works with vectors and arrays.

matrix_inverse(A,B)

Builtin matrix inversion of an array. Stores the inverse of A in B. A and
B must be standalone 2 dimensional array variables with
matching dimensions. B can be the same as A. Returns a value, 1 for success, 0 for failure
or singular matrix.

matrix_determinant(A)

Builtin matrix determinant of a square array.
Has function syntax, so it returns the value of the determinant.
Syntax: det := matrix_determinant(A)
Enter command: define aaa real[2][2]
Enter command: aaa[1][1] := 2; aaa[1][2] := 3; aaa[2][1] := 4; aaa[2][2] := 5
Enter command: print matrix_determinant(aaa)
2
Also works on square 2D array attributes of elements. Does not modify the array.

wrap_inverse(w)
 Inverse of symmetry group element w, in numerical
representation. Useful only if a symmetry
group has been declared in the datafile.

wrap_compose(w1,w2)
 Composition of symmetry group elements w1, w2, in
numerical
representation. Useful only if a symmetry
group has been declared in the datafile.

usrn

userdefined functions
Miscellaneous functions
IS_DEFINED
To find out if a name is already in use as a keyword or
userdefined name, use the is_defined function, which
has the syntax
IS_DEFINED(stringexpr)
The stringexpr must be a quoted string or other string expression.
The return value is 0 if the name is undefined, 1 if defined.
This function is evaluated at runtime, but variables in the whole
command are parsed before the command is executed, so a command
like if is_defined("newvar") then newvar := 1 else newvar := 2
will give newvar
the value 1 even if this is its first appearance.
A better way in scripts to test is to use the define
command to define the variable without initialization, and then test to
see if it has the default value, i.e. 0 for a numeric variable and a
sizeof 0 for a string variable.
SIZEOF
Returns the number of entries in an array or array
extra attribute.
Can also be applied to a string or string variable to get the number
of characters in the string.
Syntax:
SIZEOF(name)
SIZEOF(string)
In the first form, name is the name of the array or extra attribute,
not in quotes.
VALID_BOUNDARY
Boolean function. Returns 1 or 0 depending on whether a parametric
boundary with the given number exists (note that the name of a
named boundary is internally interpreted as a number). Syntax:
VALID_BOUNDARY(expression)
One use is in looping through all parametric boundaries, in conjunction
with the high_boundary internal variable. For example,
for ( bnum := 1 ; bnum <= high_boundary ; bnum += 1 )
if valid_boundary(bnum) then
printf "Boundary %d has %d vertices on it\n",bnum,
sum(vertex,on_boundary bnum);
VALID_CONSTRAINT
Boolean function. Returns 1 or 0 depending on whether a levelset
constraint with the given number exists (note that the name of a
named constraint is internally interpreted as a number). Syntax:
VALID_CONSTRAINT(expression)
One use is in looping through all levelset constraints, in conjunction
with the high_constraint internal variable. For example,
for ( cnum := 1 ; cnum <= high_constraint ; cnum += 1 )
if valid_constraint(cnum) then
printf "Constraint %d has %d vertices on it\n",cnum,
sum(vertex,on_constraint cnum);
VALID_ELEMENT
Boolean function.
Returns 1 or 0 depending on whether an element of a given index
exists. Syntax:
VALID_ELEMENT(indexed_element)
Examples:
if valid_element(edge[12]) then refine edge[12]
if valid_element(body[2]) then set body[2].facet color red
Userdefined builtin functions
Userdefined functions can be defined in C in userfunc.c, so
you have to be compiling your own Evolver if you want to use these.
They are meant for situations where expression interpretation
is too slow, or functions such as elliptic integrals are
wanted. Currently, they are automatically functions of
the coordinates. Do not give any arguments in the expression;
for example "(usr1 + usr3)/usr10".
Aggregate functions
The maximum, minimum, sum, or average of an expression over a set
of elements may be done with aggregate functions. The syntax is
aggregate(generator,expr)
where aggregate is max, min, sum,
or avg
,
and generator is an
element generator. Example: this
prints the total area of all green facets: print sum(facet where color == green, area)
"Count" is an aggregate function that gives the number of elements
generated, regardless of the expression.
Element attribute values in expressions
The value of any
element attribute
may be used in an expression.
The attribute name alone may be used if there is a default element active.
Example: foreach facet do print area
Otherwise the attribute is referred to as a field of the element:
foreach facet ff do print ff.area
Indexed
extra attributes
need an index in square brackets:
foreach facet ff do print ff.something[3]
Index values are rounded down to integer values. Indexing starts with 1.
Most attributes are numerical or boolean, but some are
element generators.
The following attributes are available (for details, see
elements):
 X1,X2,...,X,Y,Z,W
 Coordinates of vertices, components of
edge vector or facet normal. May also be referred to in index form as x[1], x[2], etc.
 P1,P2
 Parameters for
parametric boundaries.
 ID
 Element identifying number.
 OID
 Oriented element identifying number.
 ORIGINAL
 Number of parent datafile element.
 COLOR
 Integer representing color of facet
(color of front if back different) or edge.
 FRONTCOLOR
 Color of front of facet.
 BACKCOLOR
 Color of back of facet.
 VALENCE
 Number of edges on a vertex, facets on edge, edges on a facet, or facets, or on a body.
 AREA
 Area of facet.
 LENGTH
 Length of edge.
 VOLUME
 Actual volume of body.
 TARGET
 Target fixed volume of body.
 VOLCONST
 Constant added to calculated volume of body.
 DENSITY
 Density of edge, facet, or body.
 DIHEDRAL
 Dihedral angle of facets on an edge.
 ORIENTATION
 Sign for oriented integrals of edges or facets.
 ON_CONSTRAINT n
 True if element on given
constraint. n may be a constraint number or a constraint name.
 HIT_CONSTRAINT n
 True if element is exacty on a constraint.
Useful for
onesided constraints. n may be a constraint number or a constraint name.
 ON_BOUNDARY n
 True if element on given
boundary. n may be a boundary number or a boundary name.
 ON_QUANTITY quantityname
 True if the
given named quantity applies to the element.
 ON_METHOD_INSTANCE instancename
 True if the
given method instance applies to the element.
 WRAP
 Numerical edge wrap in
torus model or other
quotient space.
 quantity_name
 Contribution of an element to a
named quantity.
 instance_name
 Contribution of an element to a
named method instance.
 extra_attribute[expr]
 Name of userdefined
extra attribute,
with subscript if needed.
 VERTEX

Generator of edge or facet vertices.
 MIDV
 Id of edge midpoint in quadratic model.
 EDGE

Generator of edges attached to vertex, or edges around a facet.
 FACET

Generator of facets around a vertex or an edge.
 BODY

Generator of bodies that a facet is on.
Variables
The Evolver command language has its own version of the userdefined variables
common to most programming languages. Variables are typed according to
the types of the values assigned to them: numeric or string.
Users may define numeric variables either by
variable declarations in the datafile, or both types by
assigning a value
to an identifier in a command. A variable may be subjected to optimization
by declaring it an
optimizing_parameter in the datafile.
Arrays
It is possible to define multidimensional arrays of integers or reals
with the syntax
DEFINE variablename REALINTEGERSTRING [expr]...
This syntax works both in the datafile header and at the command prompt.
If the array already exists, it will be resized, with old elements
kept as far as possible. Do not resize with a different number of
dimensions. Note that array indexing starts at 1. A size of 0 is legal,
and useful if you are not using an array at the moment and want to
free storage space. There is runtime checking of array bounds. Example:
define fvalues integer[10][4]
define basecoord real[10][space_dimension]
define primcol string[3]
Identifier names declared local
can be used in array declarations in procedures and functions;
dynamic sizes can be used, but static sizes may be a bit faster
since memory doesn't need to be dynamically allocated.
In the top of the datafile, arrays may be initialized with
nested bracket initializers following the definition. For example:
define qwerty integer[4] = { 23, 45, 12, 2 }
define vmat real[3][2] = {{1,2},{3,4},{5,6}}
define primcol string[3] = {"red","green","blue"}
Initializers need not be complete; missing values will be zero.
Array elements may be assigned and referenced as is usual for programming
languages:
fvalues[3][4] := 234;
if basecoord[3][1] > 2 then print "hello world!\n";
Array initialization syntax works for runtime assignments to
arrays and array slices, including element attributes that
are arrays. The entries in the initializer must be single
numbers, not arrays. The number of dimensions on the left
and right side of the assignment must agree, but the sizes
in each dimension need not agree. Missing elements on the
right side are regarded as zero. Examples:
vertex[1].__x := { 1.2, 3.1, 4.7 }
define mat real[2][2];
mat := {{1,2},{3,4}}
The right side is evaluated each time the assignment is
executed, so the entries on the right can be any expressions
that evaluate to numbers. Assignment with += and = also
work, as does *= and /=, but note that all of these
work elementwise (i.e. *= and /= are not matrix multiplication
and division).
The print command
may be used to print whole arrays or array slices
in bracketed form. Example:
print fvalues
print fvalues[4]
There are some basic wholearray operations that permit arrays on
the left side of an assignment statement:
array := scalar
array := array
array := scalar * array
array := array + array
array := array  array
array := array * array
scalar := array * array // dot product if both rhs arrays onedimensional
Here "array" on both sides of the assignment means a single whole array;
not an arrayproducing expression or array slice.
But "scalar" can be any expression that evaluates to a single value.
For multiplication, the arrays must be twodimensional with properly
matching sizes. These operations also apply to element attributes
that are arrays.
There is also a matrix_inverse procedure and a
matrix_determinant function.
For onedimensional arrays, the * operator gives the
sum of the product of corresponding entries. Example:
print vertex[1].__velocity * facet[3].__facet_normal
Internal variables
These are predefined names for some of Evolver's internal variables.
They may be used in the same way as userdefined variables, except
the values of readonly variables may not be changed by the user.
 ambient_pressure_value
 Internal readwrite variable. Value of the external pressure in the ideal gas model.
 background
 Internal readwrite variable. Background color used
in certain screen graphics (xgraph and Windows, at the moment).
 body_count
 Internal readonly variable. Number of bodies.
 breakflag
 Internal readwrite variable.
When set to a nonzero value, causes the command interpreter
to abort and return to the command prompt. Software equivalent
of hitting the keyboard interrupt (typically CTRLC). The
break doesn't happen immediately, but at a certain point in
the interpreter loop when it periodically checks for user
interrupt. Meant for bailing out of nested commands, since
return only breaks out
of the current procedure.
 body_dissolve_count
 Internal readonly variable. Number of bodies dissolved by
dissolve command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 brightness
 Internal readonly variable. Median gray level used
in PostScript output and screen graphics.
 check_count
 Internal readonly variable.
Number of errors found by the most recent C
command.
 clock
 Internal readonly variable. Total elapsed Evolver execution
time in seconds. Reads system process elapsed time, which often has
a fairly coarse resolution of 0.01 seconds. For nanosecond timing,
see cpu_counter.
 console_title
 Internal readwrite string variable. This is the title that is
displayed on the Evolver command console window. The default value is
"Surface Evolver  datafilename" (with the name of the current datafile, of
course). Useful when you are simultaneously running various instances, and
you want to tell which is running in which console window. Just assigning
a string to console_title automatically changes the title on the window.
 constraint_tolerance
 Internal readwrite variable. When vertices are
projected to
levelset constraints,
projection by Newton's method
is repeated until the levelset function is smaller than constraint_tolerance.
Default value 1e12.
 cpu_counter
 Internal readonly variable. Processor cycle counter, available
only on systems I know how to access this (x86 for now). Gives the number
of CPU cycles since the system booted. Note that this is wall clock time,
not process time. Also note that it resets to zero when a computer
hibernates, so it is not guaranteed to be monotone increasing during the
life of a process! Also, multiple processors in a machine may not have
identical CPU counters, so the Evolver process should be assigned to
a particular processor (in Windows, this may be done in Task Manager
by setting the process "affinity" in its properties).
For process elapsed time,
see clock.
 datafilename
 Internal readonly variable. String containing name of current datafile.
 delete_count
 Internal readonly variable.
Sum of edge_delete_count
and facet_delete_count.
Kept for backwards compatibility.
 detorus_epsilon
 Internal readwrite variable
that is the tolerance for detorus to identify vertices when
detorus_sticky is toggled on.
 display_origin
 Internal readwrite vector. For a torus mode surface,
if clipped mode is in effect, the center of the clip box is
set with this array, whose dimension is the dimension of
the ambient space. This array does not exist by default,
it has to be created by the user.
Details.
 dissolve_count
 Internal readonly variable.
Sum of vertex_dissolve_count
edge_dissolve_count,
facet_dissolve_count,
and body_dissolve_count.
Kept for backwards compatibility.
 date_and_time
 Internal readonly variable. String containing current date and time.
 edge_count
 Internal readonly variable. Number of
edges.
 edge_delete_count
 Internal readonly variable. Number of edges deleted by
delete command.
This does not count the secondary edge deletions caused by deleting
an edge.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 edge_dissolve_count
 Internal readonly variable. Number of edges dissolved by
dissolve command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 edge_refine_count
 Internal readonly variable. Number of edges refined by
refine edges command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 edge_pop_count
 Internal readonly variable. Number of edges popd by
pop edges,
o, or
O,
commands.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 edgeswap_count
 Internal readonly variable. Number of edges swapped by
edgeswap command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 eigenneg
 Internal readonly variable. Number of negative eigenvalues in last
Hessian
factoring.
 eigenpos
 Internal readonly variable. Number of positive eigenvalues in last
Hessian
factoring.
 eigenvalues[]
 Internal readonly array. Contains the list of eigenvalues
produced by the ritz command. Example:
print eigenvalues[2]
 eigenzero
 Internal readonly variable. Number of zero eigenvalues in last
Hessian factoring.
 equi_count
 Internal readonly variable. Number of edges flipped by
equiangulation.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 estimated_change
 Internal readonly variable. Estimated
change of energy during last iteration with
estimate option in effect.
 facet_count
 Internal readonly variable. Number of
facets.
 facetedge_count
 Internal readonly variable. Number of
facetedges.
 facet_delete_count
 Internal readonly variable. Number of facets deleted by
delete command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 facet_dissolve_count
 Internal readonly variable. Number of facets dissolved by
dissolve command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 facet_refine_count
 Internal readonly variable. Number of facets refined by
refine facets command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 fix_count
 Internal readonly variable. Number of elements fixed by
fix command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 graphics_title
 Internal readwrite string variable.
This is the title that is
displayed on the Evolver graphics window. The default value is
the datafile name. Useful when you are simultaneously running various instances, and
you want to tell which is running in which graphics window. Just assigning
a string to graphics_title automatically changes the title on the window.
There are also graphics_title2 and graphics_title3 variables if you
have a second or third graphics window.
 gravity_constant
 Internal readwrite variable. Value of the gravitational
constant, which can also be set by the G
command.
 hessian_epsilon
 Internal readwrite variable. Magnitude regarded as zero by
hessian command when factoring
the Hessian matrix. If a zero appears on the diagonal at the pivot
during factoring, a check is made to see if the rest of the row is zero.
If it is, then a 1 is placed on the diagonal; else an error is reported.
 hessian_slant_cutoff
 Internal readwrite variable.
Hessian commands treat vertices whose normal
vector is nearly perpendicular
to constraints as fixed. hessian_slant_cutoff is the cosine
of angle. Works on vertices with one degree of freedom in
hessian_normal mode. Default value 0.
 high_boundary

Internal readonly variable giving the number of the highest
parametric boundary defined. Remember that the name of a named
boundary is internally interpreted as a number, and that boundary
may be referred to by that number. Useful in iterating through
all boundaries, for example
for ( bnum := 1 ; bnum <= high_boundary ; bnum += 1 )
if valid_boundary(bnum) then
printf "Boundary %d has %d vertices on it\n",bnum,
sum(vertex,on_boundary bnum);
 high_constraint

Internal readonly variable giving the number of the highest
levelset constraint. Remember that the name of a named
constraint is internally interpreted as a number, and that constraint
may be referred to by that number. Useful in iterating through
all constraints, for example
for ( cnum := 1 ; cnum <= high_constraint ; cnum += 1 )
if valid_constraint(cnum) then
printf "Constraint %d has %d vertices on it\n",cnum,
sum(vertex,on_constraint cnum);
 instance_name.modulus
 Internal readwrite variable.
Modulus of a
named method instance.
 instance_name.value
 Internal readonly variable. Value of a
named method instance.
 inverse_periods[expr][expr]

Internal readonly variable. Inverse matrix of the
torus_periods matrix. Uses 1based indexes.
Useful for normalizing vertex coordinates to period basis.
The syntax for calculating the period basis coordinates would be like
define perx real[space_dimension];
perx := vertex[1].__x * inverse_periods
 integral_order
 Internal readwrite variable.
Order of polynomial done by 1D and 2D Gaussian integration.
Much better to set 1D and 2D separately.
Synonym: integration_order

integral_order_1d
 Internal readwrite variable.
Order of polynomial done by 1D Gaussian integration.
Synonym: integration_order_1D

integral_order_2d
 Internal readwrite variable.
Order of polynomial done by 2D Gaussian integration.
Synonym: integration_order_2D
 iteration_counter

Internal readonly variable. Loop count of last loop in a command.
 jiggle_temperature
 Internal readonly variable. Current temperature for
jiggling.
 lagrange_order
 Internal readonly variable.
Order of Lagrange model.
Set with the lagrange
n command.
 last_eigenvalue
 Internal readonly variable. Eigenvalue from last
saddle or
ritz command.
 last_error
 Internal readwrite
variable. Has error number of last error message.
 last_hessian_scale
 Internal readonly variable. Stepsize from last
saddle or
hessian_seek command.
 linear_metric_mix
 Internal readwrite variable.
Fraction of linear interpolation in
Hessian metric.
 memory_arena
 Internal readonly variable.
Total memory allocated to the program's heap. Available only
on SGI and Win32 versions.
 memory_used
 Internal readonly variable.
Total memory used in the program's heap. Available only
on SGI and Win32 versions.
 notch_count
 Internal readonly variable. Number of edges notched in last
notch command.
 pickvnum
 Internal readwrite variable. Number of last vertex
picked
in the graphics window.
 pickenum
 Internal readwrite variable. Number of last edge
picked
in the graphics window.
 pickfnum
 Internal readwrite variable. Number of last facet
picked
in the graphics window.
 pop_count
 Internal readonly variable.
Sum of vertex_pop_count and
edge_pop_count. Kept for
backwards compatibility.
 pop_edge_to_tri_count
 Internal readonly variable. Number of edges flipped to triangles by
the pop_edge_to_tri command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 pop_quad_to_quad_count
 Internal readonly variable. Number of quadrilaterals flipped by
the pop_quad_to_quad command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 pop_tri_to_edge_count
 Internal readonly variable. Number of triangles flipped to edges by
the pop_tri_to_edge command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 quadratic_metric_mix
 Internal readwrite variable.
Fraction of linear interpolation in
Hessian metric in the
quadratic model. Not very useful.
 quantity_name.modulus
 Internal readwrite variable.
Modulus of a
named quantity.
 quantity_name.pressure
 Internal readonly variable.
Lagrange multiplier for
a constrained named quantity.
 quantity_name.target
 Internal readwrite variable. Constrained value of a
named quantity.
 quantity_name.value
 Internal readonly variable. Value of a
named quantity.
 random
 Internal readonly variable.
Random number between 0 and 1.
 random_seed
 Internal readwrite variable. Seed for random number
generator, used for example in jiggling
or in finding random initial vectors in various
Hessian eigenvector algorithms.
Defaults to 1 at start of datafile.
 refine_count

Internal readonly variable. Number of elements refined in last refine command.
 rotation_order
 Internal readwrite variable. Order of rotation group
for symmetry groups rotate and
flip_rotate.
 scale
 Internal readwrite variable. Current scale factor for
multiplying the force to get the motion in the
'
g
' command.
 scale_scale
 Internal readwrite variable. Multiplier for the
scale factor used in the
'
g
' command. Default
value 1.
 scrollbuffersize
 Internal readwrite variable.
The command window scroll buffer size on Windows
machines. Meant for nonNT Windows that don't
have menu properties option for this.
 self_sim_coeff
 Internal readwrite variable.
Used as magnitude coefficent when
self_similar is toggled on.
 simplex_representation
 Internal readonly variable. Whether
the simplex model is in effect.
 space_dimension
 Internal readonly variable.
Dimension of ambient space.
 sq_curvature_modulus
 Internal readwrite variable.
Multiplier for the
squared_curvature energy when it is declared the old way
in the top of the datafile.
 string_curve_tolerance
 Internal readwrite variable.
In the quadratic model,
the smoothness of graphing of curved quadratic edges can be
controlled with the internal variable
string_curve_tolerance
,
which is the desired angle in degrees between successive graphed segments
making up the edge.
 surface_dimension
 Internal readonly variable. Dimension of surface.
 symmetry_group
 Internal readonly variable. Whether any
symmetry group is active (Boolean).
 t1_edgeswap_count
 Internal readonly variable. Number of edges swapped by
t1_edgeswap command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 target_tolerance
 Internal readwrite variable.
When volume constraints
or named quantity
constraints are enforced,
Newton's method is repeated until the total deviation from target values
is less than
target_tolerance
. Default value 1e4.
 temperature
 Internal readonly variable.
Amplitude for jigglinge.
 thickness
 Internal readonly variable.
Thickness for thickened surfaces in graphics output in
P command. Used when facet
frontcolor and
backcolor are different.
Default value 0.001 times the maximum linear dimension of the surface.
If you get backside color showing through,
increase the thickness.
 torus
 Internal readonly variable. Whether
the torus model is in effect. (Boolean).
 torus_periods[expr][expr]

Internal readonly variable. Current values of the period vectors in the
torus model. Torus_periods[i][j]
is component j of vector i. Uses 1 based indexes.
For changing the torus_periods, define the
periods in the datafile with variables, and alter the variables.
 total_area
 Internal readonly variable. Total area of the surface
in soapfilm or
simplex models.
Beware that this is not continuously updated with every
change in the surface, but rather upon return to the command prompt. If
a script needs the current total_area recalculated, it should do the
"recalc" command before using total_area.
 total_energy
 Internal readonly variable. Total energy of the surface.
Beware that this is not continuously updated with every
change in the surface, but rather upon return to the command prompt. If
a script needs the current total_energy recalculated, it should do the
"recalc" command before using total_energy.
 total_length
 Internal readonly variable. Total length of the surface
in the string model.
 total_time
 Internal readonly variable. Elapsed evolution time in the form of
total scale factors.
 transform_count
 Internal readonly variable. Number of image transforms
active, as generated by the
transform_expr
command.
 fix_count
 Internal readonly variable. Number of elements unfixed by
unfix command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 vertex_count
 Internal readonly variable. Number of vertices.
 vertex_dissolve_count
 Internal readonly variable. Number of vertices dissolved by
dissolve command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 vertex_pop_count
 Internal readonly variable. Number of vertices popped by
pop or
o command.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 view_transforms_unique_point
 Internal readwrite vector variable. Used by
view_transforms_use_unique_point mode for the definition of duplicate view transforms.
 where_count
 Internal readonly variable. Number of items satisfying last
where
condition.
Prints and resets to 0 at the end of a command execution, or when
flush_counts is done.
Also reset by reset_counts.
 window_aspect_ratio
 Internal readwrite variable. The ratio of the the vertical to
horizontal dimensions of the display window. If set, this locks the
aspect ratio to the given value. The window may be resized with the
mouse, but the aspect ratio will stay the same. The unset value of
window_aspect_ratio is 0; setting window_aspect_ratio to 0 will
unlock the aspect ratio. Applies also to the PostScript bounding box,
if full_bounding_box is on.
Currently implemented only in Evolver with GLUT graphics.
Caveat: the window doesn't always fully follow the mouse; just keep trying.
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Index.