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<P>&nbsp;
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<P>
<B><FONT SIZE="5">Chapter 6</FONT></B></P>
<PRE><B><FONT SIZE="4"></FONT></B> 6.1 <A HREF="#6.1">Basic Definitions</A>
6.2 <A HREF="#6.2">Functions and Terminals</A>
6.2.1 <A HREF="#6.2.1">Ephemeral Random Constants</A>
6.2.2 <A HREF="#6.2.2">Evaluation and Argument Functions</A>
6.3 <A HREF="#6.3">User Callbacks</A>
6.3.1 <A HREF="#6.3.1">Defining the Function Set(s)</A>
6.3.2 <A HREF="#6.3.2">Fitness Evaluation Function</A>
6.3.3 <A HREF="#6.3.3">Custom Output</A>
6.3.4 <A HREF="#6.3.4">Application Initialization</A>
6.3.5 <A HREF="#6.3.5">Output Streams</A>
6.3.6 <A HREF="#6.3.6">Checkpoint Files</A>
6.4 <A HREF="#6.4">Order of Processing</A>
6.5 <A HREF="#6.5">Kernel Considerations
</A> 6.5.1 <A HREF="#6.5.1">Memory Allocation</A>
6.5.2 <A HREF="#6.5.2">Using Parameters</A>
<HR></PRE>
<P>
<B><FONT SIZE="5">Implementing Problems</FONT></B></P>
<P>
This chapter documents how to implement a new problem in lil-gp.
There are five files that the user must write. A set of skeleton
user files is provided in the distribution, it is suggested that
you copy these files and modify them to create a new problem.
</P>
<P>
Throughout this chapter, the term &quot;function&quot; refers
to functions in the GP sense. &quot;C function&quot; refers to
a function in the C language</P>
<P>
User-written code can be divided into two categories: C functions
implementing functions and terminals, and user callbacks. The
user callbacks, usually placed in the <B>app.c</B> file, do application-
specific tasks like function set initialization, calculation of
fitness, etc. The other group of C functions, usually placed in
<B>function.c</B>, are the code that is called by the kernel during
tree evaluation. <BR>
</P>
<P>
<B><FONT SIZE="4"><A NAME="6.1">6.1 Basic Definitions</A></FONT></B></P>
<P>
There are two defined constants that the kernel of lil-gp needs
in <B>appdef.h</B>. They are<FONT SIZE="2">:<BR>
</FONT>
</P>
<TABLE BORDER="2" ALIGN="DEFAULT" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">constant</TD>
<TD ALIGN="LEFT" VALIGN="TOP">value</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%"><B>MAXARGS </B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">the maximum number of arguments (children)
for any function</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%"><B>DATATYPE</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">the C data type returned by all functions
and terminals</TD>
</TR>
</TABLE>
<P>&nbsp;</P>
<P>
This is also a good place to put any application-specific <B>#defines</B>
that you may need. It is suggested that all application defines
be prefixed with <B>APP_ </B>so as not to conflict with any current
or future kernel defines.</P>
<P>
If your problem requires a more complex data type than the ones
available in C, you can use <B>typedef</B> to create a new type.
For instance, the lawnmower problem uses an ordered pair of integers
as its <B>datatype</B>. Its <B>appdef.h</B> file contains:</P>
<PRE>
<B>typedef struct</B>
<B>{</B>
<B> short x;</B>
<B> short y;</B>
<B>} vector;</B>
<B>#define DATATYPE vector<BR>
</B>
</PRE>
<P>
<B><FONT SIZE="4"><A NAME="6.2">6.2 Functions and Terminals</A></FONT></B></P>
<P>
For every ordinary function and terminal in your problem, you
write a C function to implement the action of that node. These
C functions are placed in the file <B>function.c</B>, and prototypes
for them should be placed in <B>function.h</B>.</P>
<P>
Each C function is passed two arguments, an <B>int</B> and a <B>(farg
*)</B>. What it does with these arguments depends on whether it
is implementing a function or a terminal, and if it is a function,
what type of function. All these C functions should return the
user-defined type <B>DATATYPE</B>.</P>
<P>
There are two types of functions, referred to in lil-gp as types
&quot;DATA&quot; and &quot;EXPR&quot;. If the function is of type
DATA, then when it is found in a tree, all its children will be
evaluated and their return values passed to the user code implementing
the function. The LISP equivalent of this is to implement the
function with a <B>defun</B>. If the lil-gp function is of type
EXPR, then the user code is passed pointers to its children, which
it can then ask the kernel to evaluate if needed. It can evaluate
each child as many times as appropriate, or not at all. The LISP
equivalent of this type would be to implement the function with
a <B>defmacro</B>. Use of the correct type in lil-gp is important,
especially when the evaluation of functions and terminals have
global side effects (for instance, where the evolved program is
controlling a simulation).</P>
<P>
If the function is of type DATA, it can ignore the <B>int</B>
passed to it. The <B>(farg *)</B> argument will be an array of
arguments, one element for each child. The C function should reference
the <B>d</B> field of each element to get that child's value.
For instance, consider the two-argument addition function from
the regression problem:</P>
<PRE>
<B>DATATYPE f_add ( int tree, farg *args </B>
<B>{</B>
<B> return args[0].d + args[1].d;</B>
<B>}<BR>
</B></PRE>
<P>
When this function occurs in evaluating a tree, the lil-gp kernel
will evaluate the children, store their values in the <B>args</B>
array, and call this C function.</P>
<P>
Now consider another example: the <B>IF_FOOD_AHEAD</B> function
from the artificial ant problem. It has two arguments_the first
should be evaluated if there is food in front of the ant, the
second otherwise. If type DATA were to be used for this function,
then both would be evaluated and only their return values passed
to the function (which would be doubly useless in this case, since
all the functions and terminals in the ant problem ignore the
return value). We want to let the function itself choose which
child to evaluate. This function must be of type EXPR:<BR>
</P>
<PRE>
<B>DATATYPE f_if_food_ahead ( int tree, farg *args )</B>
<B>{</B>
<B> if ( ... ) /* determine if there is food ahead */</B>
<B> evaluate_tree ( args[0].t, tree );</B>
<B> else</B>
<B> evaluate_tree ( args[1].t, tree );</B>
<B>}<BR>
</B></PRE>
<P>
For type EXPR functions, the t field of each array element should
be accessed-it is a pointer to the corresponding child. This pointer
can be passed to the <B>evaluate_tree()</B> C function to actually
do the evaluation. <B>evaluate_tree()</B> also needs to be passed
the integer argument (called <B>tree</B> in this case).</P>
<P>
C functions implementing terminals should ignore both arguments
passed to them. A simple example is the independent variable terminal
<B>X</B> from the symbolic regression problem:<BR>
</P>
<PRE>
<B>DATATYPE f_indepvar ( int tree, farg *args )</B>
<B>{</B>
<B> return g.x;</B>
<B>}<BR>
</B></PRE>
<P>
This function just returns the value of the independent variable
for the current fitness case, which has previously been stored
in a global variable by the application fitness evaluation function.<FONT SIZE="2">
<BR>
</FONT>
</P>
<P>
<B><FONT SIZE="4"><A NAME="6.2.1">6.2.1 Ephemeral Random Constants</A></FONT></B></P>
<P>
To create a terminal that acts as an ephemeral random constant,
you need to write two C functions. One will generate a new constant,
and one will print its value to a string. The first is passed
a pointer to a <B>DATATYPE</B>; it should generate a new value
and place it in the pointer.<BR>
</P>
<PRE>
<B>void f_erc_generate ( DATATYPE *r )</B>
<B>{</B>
<B> *r = random_double() * 10.0;</B>
<B>}<BR></B></PRE>
<P>
This function generates a random real number in the interval [0;
10) (assuming that <B>DATATYPE</B> is defined to be <B>double</B>
or some compatible type.</P>
<P>
The second function is used when printing out individuals. It
is passed a <B>DATATYPE</B> value. It should create a string representing
that value and return it. Typically this will print the value
into a buffer and return the buffer's address. The buffer should
be declared static_it should not be dynamically allocated (as
there is no code to free it). An example:<BR>
</P>
<PRE>
<B>char *f_erc_print ( DATATYPE v )</B>
<B>{</B>
<B> static char buffer[20];<BR></B>
<B> sprintf ( buffer, &quot;%.5f&quot;, v );</B>
<B> return buffer;</B>
<B>}<BR></B></PRE>
<P>
assuming again that DATATYPE is double or something compatible,
this will print the value to five decimal places.<BR>
</P>
<P>
<B><A NAME="6.2.2">6.2.2 Evaluation and Argument Functions</A></B></P>
<P>
No user code needs to be written to support the ADF functions
or corresponding argument termi- nals. Special entries are made
in the function table for them, and the kernel handles the evaluation
internally</P>
<P>
Evaluation functions with arguments have type DATA or EXPR, just
like ordinary functions. If the type is DATA, when the evaluation
function is hit, each child is evaluated once, and the return
values are made available via the argument terminals in the evaluated
tree. If the type is EXPR, then the children are evaluated only
when the evaluation of the target tree hits the appropriate argument
terminal (and if the same argument terminal is hit multiple times,
the child is reevaluated each time).<BR>
</P>
<P>
<B><FONT SIZE="4"><A NAME="6.3">6.3 User Callbacks</A></FONT></B></P>
<P>
Only two of the user callbacks listed here are required to do
anything <B>(app_build_function_sets()</B> to create the function
set(s) and<B> app_eval_fitness()</B> to evaluate individuals).
All the others must be present, but they can be just stubs if
you don't want to make use of them.<BR>
</P>
<P>
<B><A NAME="6.3.1">6.3.1 Defining the Function Set(s)</A></B></P>
<P>
The first user callback required is <B>app_build_function_sets()</B>.
This C function creates tables for each function set. There may
be more than one function set when individuals are represented
by multiple trees, since each tree can have its own function set.
Each function set is an array of type <B>function</B>. The following
tables show, for each type of node, what the eight fields of the
corresponding function structure should be. Some general rules
apply:<BR>
</P>
<UL>
<LI>The <B>code</B>, <B>ephem_gen</B>, and <B>ephem_str</B> fields
are C function pointers, not strings. You put the name of the
function you
</LI>
<LI>are referencing here, but don't quote it. <BR>
</LI>
<LI>The <B>string</B> field is the name of the function as a string.
It is what gets printed to represent the node when trees are printed
to output files. Names may not contain whitespace or any of the
characters `:', `(', `)', `[', `]'.<BR>
</LI>
<LI>The <B>index</B> field should always be zero.<BR>
</LI>
</UL>
<P ALIGN="center">ordinary function
</P>
<CENTER><TABLE BORDER="2" ALIGN="center" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">code </TD>
<TD ALIGN="LEFT" VALIGN="TOP">The C function implementing the function.</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_gen</TD>
<TD ALIGN="LEFT" VALIGN="TOP">
NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_str</TD>
<TD> NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%">arity</TD>
<TD>
The arity of the function (greater than zero).</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">string</TD>
<TD>
The name of the function.</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">type</TD>
<TD>FUNC_DATA or FUNC_EXPR, as appropriate.</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">evaltree</TD>
<TD>-1</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">index</TD>
<TD>0</TD>
</TR>
</TABLE></CENTER>
<P ALIGN="center">
ordinary terminal</P>
<CENTER><TABLE BORDER="2" ALIGN="center" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%">code </TD>
<TD ALIGN="LEFT" VALIGN="TOP">The C function implementing the function.</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_gen</TD>
<TD ALIGN="LEFT" VALIGN="TOP">
NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_str</TD>
<TD> NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">arity</TD>
<TD>
0</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">string</TD>
<TD>
The name of the terminal</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">type</TD>
<TD>TERM_E</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">evaltree</TD>
<TD>-1</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">index</TD>
<TD>0</TD>
</TR>
</TABLE></CENTER>
<BR>
<P ALIGN="center"><FONT SIZE="2"><BR>
</FONT>
</P>
<P ALIGN="center">ephemeral random constant terminal</P>
<CENTER><TABLE BORDER="2" ALIGN="center" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%">code </TD>
<TD ALIGN="LEFT" VALIGN="TOP">NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_gen</TD>
<TD ALIGN="LEFT" VALIGN="TOP">
<FONT SIZE="2">The C function to generate new random
values.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_str</TD>
<TD> <FONT SIZE="2">The C function to print values to a string.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">arity</TD>
<TD>
0</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">string</TD>
<TD>
<FONT SIZE="2">The generic name of the terminal. (Printed
trees will</FONT><FONT SIZE="2">almost always have the string representing the
value of</FONT><FONT SIZE="2">the terminal, rather than this name.</FONT>
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">type</TD>
<TD>TERM_ERC</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">evaltree</TD>
<TD>-1</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">index</TD>
<TD>0</TD>
</TR>
</TABLE></CENTER>
<BR>
<P>&nbsp;</P>
<P ALIGN="center">
evaluation function/terminal</P>
<CENTER><TABLE BORDER="2" ALIGN="center" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%">code </TD>
<TD ALIGN="LEFT" VALIGN="TOP">NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_gen</TD>
<TD ALIGN="LEFT" VALIGN="TOP">
NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_str</TD>
<TD> NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">arity</TD>
<TD>
<FONT SIZE="2">-1. (The kernel will determine the arity
by looking</FONT><FONT SIZE="2">at the argument terminals in the target tree.)</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">string</TD>
<TD>
<FONT SIZE="2">The name of this function/terminal.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">type</TD>
<TD><FONT SIZE="2">EVAL_DATA or EVAL_EXPR, as appropriate.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">evaltree</TD>
<TD><FONT SIZE="2">The number of the tree to evaluate when
this function is hit.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">index</TD>
<TD>0</TD>
</TR>
</TABLE></CENTER>
<BR>
<P ALIGN="center">
argument terminal</P>
<CENTER><TABLE BORDER="2" ALIGN="center" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="15%">code </TD>
<TD ALIGN="LEFT" VALIGN="TOP">NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_gen</TD>
<TD ALIGN="LEFT" VALIGN="TOP">
NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">ephem_str</TD>
<TD> NULL</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">arity</TD>
<TD>
0</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">string</TD>
<TD>
<FONT SIZE="2">The name of this terminal.</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">type</TD>
<TD><FONT SIZE="2">TERM_ARG</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">evaltree</TD>
<TD><FONT SIZE="2">The argument number (which child of the
corresponding</FONT><FONT SIZE="2">evaluation function this terminal represents).</FONT></TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%">index</TD>
<TD>0</TD>
</TR>
</TABLE></CENTER>
<BR>
<P>
The function sets for the lawnmower problem contain examples of
all five types of node<FONT SIZE="2">:<BR>
</FONT>
</P>
<PRE>
<B>function sets[3][10] =
</B>
<B> /*** RPB ***/</B>
<B>{ { { f_left, NULL, NULL, 0, &quot;left&quot;, TERM_NORM, -1,0 },</B>
<B> { f_mow, NULL, NULL, 0, &quot;mow&quot;, TERM_NORM, -1, 0 },</B>
<B> { NULL, f_vecgen, f_vecstr, 0, &quot;Rvm&quot;, TERM_ERC, -1,0 },</B>
<B> { f_frog, NULL, NULL, 1, &quot;frog&quot;, FUNC_DATA, -1, 0},</B>
<B> { f_vma, NULL, NULL, 2, &quot;vma&quot;, FUNC_DATA, -1, 0 },</B>
<B> { f_prog2, NULL, NULL, 2, &quot;prog2&quot;, FUNC_DATA, -1,0 },</B>
<B> { NULL, NULL, NULL, -1, &quot;ADF0&quot;, EVAL_DATA, 1, 0 },</B>
<B> { NULL, NULL, NULL, -1, &quot;ADF1&quot;, EVAL_DATA, 2, 0 }},<BR>
</B>
<B>/*** ADF0 ***/</B>
<B>{ { f_vma, NULL, NULL, 2, &quot;vma&quot;, FUNC_DATA, -1, 0},</B>
<B> { f_prog2, NULL, NULL, 2, &quot;prog2&quot;, FUNC_DATA, -1,0 },</B>
<B> { f_left, NULL, NULL, 0, &quot;left&quot;, TERM_NORM, -1, 0},</B>
<B> { f_mow, NULL, NULL, 0, &quot;mow&quot;, TERM_NORM, -1, 0 },</B>
<B> { NULL, f_vecgen, f_vecstr, 0, &quot;Rvm&quot;, TERM_ERC, -1,0 } },<BR>
<BR>
</B>
<B>/*** ADF1 ***/</B>
<B>{ { f_left, NULL, NULL, 0, &quot;left&quot;, TERM_NORM, -1,0 },</B>
<B> { f_mow, NULL, NULL, 0, &quot;mow&quot;, TERM_NORM, -1, 0 },</B>
<B> { NULL, f_vecgen, f_vecstr, 0, &quot;Rvm&quot;, TERM_ERC, -1,0 },</B>
<B> { NULL, NULL, NULL, 0, &quot;ARG0&quot;, TERM_ARG, 0, 0 },
<BR></B>
<B> { f_frog, NULL, NULL, 1, &quot;frog&quot;, FUNC_DATA, -1, 0},</B>
<B> { f_vma, NULL, NULL, 2, &quot;vma&quot;, FUNC_DATA, -1, 0 },</B>
<B> { f_prog2, NULL, NULL, 2, &quot;prog2&quot;, FUNC_DATA, -1,0 },</B>
<B> { NULL, NULL, NULL, -1, &quot;ADF0&quot;, EVAL_DATA, 1, 0 }} };<BR>
<BR></B></PRE>
<P>
This problem uses two ADFs-the zero-argument ADF0 and the one-argument
ADF1. Both ADFs are available to the result-producing branch.
In addition, ADF0 can be called from within ADF1</P>
<P>
Note that the functions and terminals can appear in the table
in any order. Previous versions of lil-gp required all functions
to appear first in the table, followed by the terminals, but this
is no longer the case</P>
<P>
Once the function table is created, a list of function sets needs
to be created that references it. You should create an array of
type <B>function_set</B> with one member for each function set.
The size field should be set to the number of functions and terminals
in it, and the <B>cset</B> field should point to the function
table. The lawnmower problem uses:<BR>
</P>
<PRE>
<B>function_set *fset;</B>
<B>. . . .</B>
<B>fset = (function_set *)MALLOC ( 3 * sizeof ( function_set ));</B>
<B>fset[0].size = 8;</B>
<B>fset[0].cset = sets[0];</B>
<B>fset[1].size = 5;</B>
<B>fset[1].cset = sets[1];</B>
<B>fset[2].size = 8;</B>
<B>fset[2].cset = sets[2];<BR></B></PRE>
<P>
Next you must build a tree <I>map</I>, indicating which trees
use which function sets. This is just an array of <B>ints</B>,
where the <I>n</I>th element indicates the number of the function
set of the <I>n</I>th tree. In the case of the lawnmower problem,
there is just one tree per function set:</P>
<PRE>
<B>tree_map = (int *)MALLOC ( 3 * sizeof ( int ) );</B>
<B>tree_map[0] = 0;</B>
<B>tree_map[1] = 1;</B>
<B>tree_map[2] = 2;<BR></B></PRE>
<P>
If two trees use the same function set, then crossover may exchange
genetic material between these trees on different individuals.
If this is not desired, you can make a copy of the function set,
and have one tree use the copy. This would be accomplished with
something like:</P>
<PRE>
<B>fset[2].size = 8;</B>
<B>fset[2].cset = sets[2];</B>
<B>fset[3].size = 8;</B>
<B>fset[3].cset = sets[2]; /* note they refer to the same functions*/</B>
<B>. . .</B>
<B>tree_map[2] = 2;</B>
<B>tree_map[3] = 3;<BR></B></PRE>
<P>
Now trees 2 and 3 will not crossover with each other, even though
their function sets are identical</P>
<P>
One last thing to build is a list of tree names--these will be
used to label the separate trees when individuals are printed
out:</P>
<PRE>
<B>char *tree_name[3];</B>
<B>. . .</B>
<B>tree_name[0] = &quot;RPB&quot;;</B>
<B>tree_name[1] = &quot;ADF0&quot;;</B>
<B>tree_name[2] = &quot;ADF1&quot;;<BR></B></PRE>
<P>
Now that all the data structures are built, you must pass them
as arguments to the kernel function <B>function_sets_init().</B>
This function will do some validity checking and make internal
copies of everything. After this function returns, you may destroy
your copies. You should also save the return value of this function
(an <B>int</B>) and return it to the kernel.</P>
<PRE>
<B>int ret;</B>
<B>. . .</B>
<B>ret = function_sets_init ( fset, 3, tree_map, tree_name, 3);<BR>
</B>
<B>FREE ( tree_map );</B>
<B>FREE ( fset ) ;<BR>
</B>
<B>return ret;<BR></B></PRE>
<P>
The second argument to <B>function_sets_init()</B> is the number
of function sets, the fifth argument is the number of trees per
individual.<BR>
</P>
<P>
<B><A NAME="6.3.2">6.3.2 Fitness Evaluation Function</A></B></P>
<P>
The user function <B>app_eval_fitness()</B> is called whenever
an individual is to be evaluated. It is passed a pointer to an
individual structure. It should fill in these fields:</P>
<P>
<B>r_fitness</B> The raw fitness.<BR>
</P>
<P>
<B>s_fitness</B> The standardized fitness (all values nonnegative,
a perfect individual is zero).<BR>
</P>
<P>
<B>a_fitness</B> The adjusted fitness (lies in the interval [0;
1], a perfect individual is one).<BR>
</P>
<P>
<B>hits</B> The auxiliary hits measure.<BR>
</P>
<P>
<B>evald</B> Always set this to <B>EVAL_CACHE_VALID</B> to indicate
that the fitness fields are valid.<BR>
</P>
<P>
The function should call <B>set_current_individual()</B> with
the pointer passed to it before doing any evaluations. The function
can evaluate trees of the individual by calling <B>evaluate_tree()</B>,
passing it a pointer to the tree data <I>and</I> the tree number.
</P>
<P>
Typically the function will iterate over all the fitness cases.
The global variable g, which is a user-defined structure, is used
to pass information between <B>app_eval_fitness()</B> and the
functions and terminals. For example, in the symbolic regression
problem, <B>g.x</B> is set to the <I>x </I>value for the current
fitness case, then the tree is evaluated. When the evaluation
reaches the independent variable terminal, the C function implementing
it simply reads this value and returns it.</P>
<P>
A typical evaluation function will have this general structure:
</P>
<PRE>
<B>void app_eval_fitness ( individual *ind )</B>
<B>{</B>
<B> set_current_individual ( ind );</B>
<B> . . .</B>
<B> for ( &lt;loop over fitness cases&gt; )</B>
<B> {</B>
<B> &lt;set up global structure for current fitness case&gt;<BR>
</B>
<B> /* here we evaluate tree 0, but you can evaluate any tree of</B>
<B> * the individual as many times as you like.</B>
<B> */</B>
<B> value = evaluate_tree ( ind-&gt;tr[0].data, 0 );</B>
<B> . . .</B>
<B> }<BR>
</B>
<B> ind-&gt;hits = &lt;whatever&gt;;</B>
<B> ind-&gt;r_fitness = &lt;whatever&gt;;</B>
<B> ind-&gt;s_fitness = &lt;whatever&gt;;</B>
<B> ind-&gt;a_fitness = &lt;whatever&gt;;<BR>
</B>
<B> /* indicate that the fitness fields are correct.*/</B>
<B> ind-&gt;evald = EVAL_CACHE_VALID;</B>
<B>}<FONT SIZE="2"><BR></FONT></B></PRE>
<P>
More complex problems which require a simulation store the entire
state of the simulation in <B>g. app_eval_fitness()</B> resets
the simulation, before evaluating the tree. For instance, in the
artificial ant problem the tree is evaluated repeatedly until
the time expires or all the food has been collected</P>
<P>
The functions and terminals read and modify the global state information
in order to simulate the ant's senses and movements.<BR>
</P>
<P>
<B><A NAME="6.3.3">6.3.3 Custom Output</A></B></P>
<P>
After every the evaluation of each generation, lil-gp calls the
function <B>app_end_of_evalulation()</B>. It is passed the generation
number, a pointer to the entire population, statistics for the
run and generation, and a flag indicating whether a new best-of-run
individual has been found or not. It should return a 1 or 0, indicating
whether the user termination criterion has been met and the run
should stop</P>
<P>
Suppose the that the function is declared with the following argument
names<FONT SIZE="2">:</FONT></P>
<PRE>
<B>int app_end_of_evaluation ( int gen, multipop *mpop, int newbest,</B>
<B>popstats *gen_stats, popstats *run_stats )<BR>
</B></PRE>
<P>
The population is passed as the pointer to a structure of type
<B>(multipop *)</B>. Everything within this structure should be
treated as read-only. This table gives some useful items of information
stored in this structure:</P>
<P>&nbsp;</P>
<TABLE BORDER="2" ALIGN="DEFAULT" WIDTH="100%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;size</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">number of subpopulations
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;size</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">size of population p
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i]</B> </TD>
<TD ALIGN="LEFT" VALIGN="TOP">the i'th individual of population
p
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i].r_fitness</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">raw fitness of individual
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i].s_fitness</B> </TD>
<TD ALIGN="LEFT" VALIGN="TOP">standardized fitness
of individual
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i].a_fitness</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">adjusted fitness of
individual
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i].hits</B> </TD>
<TD ALIGN="LEFT" VALIGN="TOP">hits of individual
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP"><B>mpop-&gt;pop[p]-&gt;ind[i].tr[n].data</B></TD>
<TD ALIGN="LEFT" VALIGN="TOP">tree n data pointer
</TD>
</TR>
</TABLE>
<P>&nbsp;</P>
<P>
The tree data pointer(s) can be passed to <B>evaluate_tree()</B>
to evaluate the tree just as in the evaluation function. To print
the entire individual, pass its address to <B>print_individual()</B>
or <B>pretty_print_individual().</B></P>
<P>
The content of the statistics structure should be discernible
to the interested reader from the declaration in <B>types.h. gen_stats[0]</B>
is statistics for the whole population in the current generation,
while <B>gen_stats[<I>i</I>]</B> gives the same just for subpopulation
<I>i</I>. The <B>run_stats</B> array is similar, but accumulates
information over the whole run</P>
<P>
In many problems it is useful to access the best-of-run or best-of-generation
individual for printing or doing extra evaluations. For instance,
the symbolic regression problem produces an extra output file
with the best-of-run individual evaluated at 200 points over the
interval of interest, for easy plotting. A copy of the best-of-run
individual is pointed to by<B> run_stats[0].best[0]-&gt;ind</B>,
and the best-of-generation individual by <B>gen_stats[0].best[0]-&gt;ind</B>.</P>
<P>
In versions of lil-gp prior to 0.99b, it was an undocumented feature
that by modifying the parameter database, the breeding parameters
could be altered dynamically during the run. If you took advantage
of this, you must now call <B>rebuild_breeding_table()</B> after
modifying the parameters, and pass it the <B>multipop</B> pointer
passed to you. If you do not, your changes to the parameter database
will have no effect. This ability is now considered a bona fide
feature of lil-gp, and will be supported in future releases</P>
<P>
Changes to the subpopulation exchange topology parameters underwent
a similar change. If you change the parameters during the run,
you should call <B>rebuild_exchange_topology()</B> after making
changes in order for them to have any effect</P>
<P>
Some kernel operations (for instance, restarting from a checkpoint
file) imply rebuilding the breeding and topology tables from the
parameter database. You should only make changes to these parameters
when you intend to immediately call the appropriate rebuilding
functions, otherwise unpredictable things will occur.</P>
<P>
Another user callback <B>app_end_of_breeding()</B> is called after
the new population is created each generation. This is passed
the generation number and the population structure, just as in
the end of evaluation callback, but no statistics information.
<BR>
</P>
<P>
<B><A NAME="6.3.4">6.3.4 Application Initialization</A></B></P>
<P>
There are two functions provided for application-specific initialization:
<B>app_initialize()</B> and <B>app_uninitialize().</B> app_initialize()
is passed an integer flag indicating whether the run is starting
from a checkpoint or not. It should return 0 to indicate success,
or anything to abort the run</P>
<P>
Initialization such as memory allocation and reading parameters
should go in <B>app_initialize().</B> The last function is called
at the end of the run, and may used to do things like free memory.<FONT SIZE="2">
<BR>
</FONT>
</P>
<P>
<B><A NAME="6.3.5">6.3.5 Output Streams</A></B></P>
<P>
An output stream is a simple abstraction of an output file. This
mechanism handles both the naming of the actual file and uses
the detail level (the <B>output.detail</B> parameter) to filter
the output. Some functions are provided for writing to output
streams:</P>
<P>
<B>oputs ( int streamid, int detail, char *string )</B> Prints
the string to the given output stream, if the value of
detail is less than or equal to the current detail level.<BR>
</P>
<P>
<B>oprintf ( int streamid, int detail, char *format, ... )</B>
Processes the <B>format</B> and succeeding arguments as in
printf(), and prints the resulting string to the stream if the
detail is less than or equal to the current detail level. <BR>
</P>
<P>
<B>test_detail_level ( int detail )</B> Returns true if the argument
is less than or equal to the current detail level.<BR>
</P>
<P>
<B>output_filehandle ( int streamid )</B> Returns the filehandle
<B>(FILE *)</B> for the given stream. Useful for passing to
<B>print_tree()</B> and the like.<BR>
</P>
<P>
The standard output files (<B>.sys, .gen</B>, etc.) are can be
printed to with the stream ids <B>OUT_SYS, OUT_GEN</B>, etc. For
instance:</P>
<PRE>
<B>oprintf ( OUT_SYS, 30, &quot;Tree %d is:&quot;n&quot;, tree_num);</B>
<B>if ( test_detail_level ( 30 ) )</B>
<B> print_tree ( tree[tree_num], output_filehandle ( OUT_SYS ));<BR></B></PRE>
<P>
An application can define custom output streams (for instance,
the <B>.fn</B> output file of the regression problem). This is
done in the application function <B>app_create_output_streams()</B>.
This function should be used <I>only</I> to create user output
streams. In it, you call <B>create_output_stream()</B> with five
arguments</P>
<P>
<B>id</B> The id for the stream (an integer). User-defined output
streams should have ids <B>OUT_USER</B>,
<B>OUT_USER+1</B>, etc. <BR>
</P>
<P>
<B>ext</B> The extension for the filename. This string is appended
to a basename (the parameter <B>output.basename</B>)
to create the filename).<BR>
</P>
<P>
<B>reset </B>A flag indicating whether the stream can be closed
and reopened (using the functions
<B>output_stream_close()</B> and <B>output_stream_open()</B>).
Reopening a stream overwrites the old file (like
the <B>.bst</B> file).<BR>
</P>
<P>
<B>mode</B> The mode string to pass to<B> fopen()</B> when opening
the file. Typically will be &quot;<B>w</B>&quot; or &quot;<B>wb</B>&quot;.
<BR>
</P>
<P>
<B>autoflush </B>Flag indicating whether the file should be flushed
after each call to <B>oputs()</B> and <B>oprintf().<BR>
</B>
</P>
<P>
<B>app_create_output_streams()</B> is called before any parameters
have been loaded, so you should not attempt to read the parameter
database in this function.<BR>
</P>
<P>
<B><A NAME="6.3.6">6.3.6 Checkpoint Files</A></B></P>
<P>
Two functions are provided for saving user state to checkpoint
files, <B>app_write_checkpoint()</B> and <B>app_read_checkpoint().</B>
Each is passed a file handle <B>(FILE *)</B> opened in text mode
for writing or reading, respectively. Each function should leave
the file pointer at the end of the user section.<BR>
</P>
<P>
<B><A NAME="6.4">6.4 Order of Processing</A></B></P>
<P>
Here is the order things happen in during a run. <BR>
</P>
<P>
print startup message
</P>
<P>initialize parameter database
</P>
<P>
initialize ERCs
</P>
<P>
initialize generation space
</P>
<P>
<B>app_create_output_streams()</B>
</P>
<P>
initialize output streams
</P>
<P>
<B>pre_parameter_defaults()</B>
</P>
<P>
process command-line arguments in order, possibly including loading
of checkpoint file
</P>
<P>
if not starting from checkpoint, <B>post_parameter_defaults()</B>
</P>
<P>
open output files
</P>
<P>
if not already done (during loading of checkpoint), <B>app_build_function_sets()</B>
</P>
<P>
read tree node/depth limits from parameters
</P>
<P>
if not starting from checkpoint, seed random number generator
</P>
<P>
<B>app_initialize()</B>
</P>
<P>
if not starting from checkpoint, create initial random population
</P>
<P>
initialize subpopulation exchange topology
</P>
<P>
initialize breeding table
</P>
<P>
run the GP: until termination
</P>
<BLOCKQUOTE>
evaluate the population, unless this is first generation after
loading checkpoint
</BLOCKQUOTE>
<BLOCKQUOTE>
compute population statistics
</BLOCKQUOTE>
<BLOCKQUOTE>
<TABLE BORDER="0" ALIGN="DEFAULT" WIDTH="50%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%"></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="100%"> <B>app_end_of_evaluation()</B></TD>
</TR>
</TABLE>
</BLOCKQUOTE>
<BLOCKQUOTE>
write checkpoint file, if necessary
</BLOCKQUOTE>
<BLOCKQUOTE>
if this is not the last generation</BLOCKQUOTE>
<BLOCKQUOTE>
<TABLE BORDER="0" ALIGN="DEFAULT" WIDTH="50%">
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%"></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="100%"> do subpopulation exchange, if necessary
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%"></TD>
<TD ALIGN="LEFT" VALIGN="TOP">breed new population
</TD>
</TR>
<TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="10%"></TD>
<TD ALIGN="LEFT" VALIGN="TOP">
<B>app_end_of_breeding()</B></TD>
</TR>
</TABLE>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TABLE BORDER="0" ALIGN="DEFAULT" WIDTH="50%">
<TR></TR>
</TABLE>
</BLOCKQUOTE>
<P>
<B>app_uninitialize()</B>
</P>
<P>
free breeding table
</P>
<P>
free subpopulation exchange topology
</P>
<P>
free population
</P>
<P>
free parameter database
</P>
<P>
free ERCs
</P>
<P>
free generation spaces
</P>
<P>
free function sets
</P>
<P>
print system statistics
</P>
<P>
close output streams<BR>
</P>
<P>
<B><FONT SIZE="4"><A NAME="6.5">6.5 Kernel Considerations</A><BR>
</FONT></B>
</P>
<P>
<B><A NAME="6.5.1">6.5.1 Memory Allocation</A></B></P>
<P>
lil-gp system has a system for tracking memory usage.1 This is
helpful in tracking down mem- ory leaks, among other things. To
use it, just use <B>MALLOC(), REALLOC()</B>, and<B> FREE()</B>
instead of <B>malloc(), realloc(),</B> and <B>free().</B> The
uppercased versions should work exactly like their low- ercased
counterparts. You may use the lowercase versions if you do not
wish to have the memory included in the statistics, but <I>do
not mix pointers</I> <I>returned by the two different sets of
functions</I>. Don't <B>FREE</B> memory that you've<B> malloc</B>'ed,
etc.<BR>
</P>
<P>
<B><A NAME="6.5.2">6.5.2 Using Parameters</A></B></P>
<P>
User code may read and write the parameter database, using the
functions<B> get_parameter()</B> and <B>add_parameter().</B> The
implementation of the database is not terribly efficient,2 so
you shouldn't, for instance, read a parameter inside the code
for a function or terminal. Reading a given parameter once per
generation should be considered a maximum. If you need the value
more often than that, you should buffer it in a C variable</P>
<P>
<B>get_parameter()</B> takes the name of the parameter (the string)
and returns a character pointer to its value, or <B>NULL</B> if
the parameter is not present in the database. You should not modify
the string returned; make a copy if you need to use it in a destructive
manner. <B>add_parameter()</B> takes the parameter name, value,
and a flag indicating whether the name or the value should be
copied, or both. Adding a parameter that is already present overwrites
the old value.<BR>
</P>
<P>
<FONT SIZE="2">1 It can be disabled completely by removing or commenting
out the line</FONT><FONT SIZE="2">&quot;#define TRACK_MEMORY&quot; from protos.h.
</FONT></P>
<P>
<FONT SIZE="2">2 Read &quot;linear search.&quot;</FONT></P>
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