File: gb_books.w

package info (click to toggle)
sgb 1:20030623-3
  • links: PTS
  • area: non-free
  • in suites: sarge
  • size: 1,868 kB
  • ctags: 28
  • sloc: makefile: 197; sh: 15
file content (545 lines) | stat: -rw-r--r-- 23,679 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
% This file is part of the Stanford GraphBase (c) Stanford University 1993
@i boilerplate.w %<< legal stuff: PLEASE READ IT BEFORE MAKING ANY CHANGES!
@i gb_types.w

\def\title{GB\_\,BOOKS}
\def\<#1>{\hbox{$\langle$\rm#1$\rangle$}}

\prerequisites{GB\_\,GRAPH}{GB\_\,IO}
@* Introduction. This GraphBase module contains the |book|
subroutine, which creates a family of undirected graphs that are based on
classic works of literature.  It also contains the |bi_book|
subroutine, which creates a related family of bipartite graphs.
An example of the use of |book| can be found in the demonstration
program {\sc BOOK\_\kern.05emCOMPONENTS}.

@(gb_books.h@>=
extern Graph *book();
extern Graph *bi_book();

@ The subroutine call |book(@[@t\<title>@>@],n,x,first_chapter,last_chapter,
in_weight,out_weight,seed)|
constructs a graph based on the information in \<title>\.{.dat},
where \<title> is either \.{"anna"} (for {\sl Anna Karenina\/}),
\.{"david"} (for {\sl David Copperfield\/}),
\.{"jean"} (for {\sl Les Mis\'erables\/}),
\.{"huck"} (for {\sl Huckleberry Finn\/}), or
\.{"homer"} (for {\sl The Iliad\/}).
Each vertex of the graph corresponds to one of the characters in the
selected book. Edges between vertices correspond to encounters between
those characters. The length of each edge is~1.

Subsets of the book can be selected by specifying that the edge data should be
restricted to chapters between |first_chapter| and |last_chapter|,
inclusive. If |first_chapter=0|, the result is the same as if
|first_chapter=1|. If |last_chapter=0| or if |last_chapter| exceeds
the total number of chapters in the book, the result is the same as
if |last_chapter| were the number of the book's final chapter.

The constructed graph will have $\min(n,N)-x$ vertices, where $N$ is the
total number of characters in the selected book.
However, if |n| is zero, |n| is automatically made equal to the maximum
possible value,~$N$. If |n| is less than~$N$, the |n-x| characters will be
selected by assigning  a weight to each character and choosing the |n| with
largest weight, then excluding the largest~|x| of these,
using random numbers to break ties in case of equal weights.
Weights are computed by the formula
$$ |in_weight|\cdot\\{chapters\_in}+|out_weight|\cdot\\{chapters\_out}, $$
where \\{chapters\_in} is the number of chapters between |first_chapter|
and |last_chapter| in which a particular character appears, and
\\{chapters\_out} is the number of other chapters in which that
character appears. Both |in_weight| and |out_weight| must be at most
1,000,000 in absolute value.

Vertices of the graph will appear in order of decreasing weight.
The |seed| parameter defines the pseudo-random numbers used wherever
a ``random'' choice between equal-weight vertices needs to be made.
As usual with GraphBase routines, different choices of |seed|
will in general produce different selections,
but in a system-independent manner; identical results will be obtained on
all computers when identical parameters have been specified.
Any |seed| value between 0 and $2^{31}-1$ is permissible.

@ Examples: The call |book("anna",0,0,0,0,0,0,0)| will construct a
graph on 138 vertices that represent all 138 characters of Tolstoy's
{\sl Anna Karenina\/}, as recorded in \.{anna.dat}. Two vertices will
be adjacent if the corresponding characters
encounter each other anywhere in the book. The call
|book("anna",50,0,0,0,1,1,0)| is similar, but it is restricted to
the 50 characters that occur most frequently, i.e., in the most chapters.
The call |book("anna",50,0,10,120,1,1,0)| has the same vertices, but it
has edges only for encounters that take place between chapter~10
and chapter~120, inclusive. The call |book("anna",50,0,10,120,1,0,0)| is
similar, but its vertices are the 50 characters that occur most often in
chapters 10 through~120, without regard to how often they occur in
the rest of the book. The call |book("anna",50,0,10,120,0,0,0)| is
also similar, but it chooses 50 characters completely at random
(possibly from those that don't occur in the selected chapters at all).

Parameter |x|, which causes the |x| vertices of highest weight to be
excluded, is usually either 0 or~1. It is provided primarily so that
users can set |x=1| with respect to {\sl David Copperfield\/} and {\sl
Huckleberry Finn}; those novels are narrated by their principal
character, so they have edges between the principal character and
almost everybody else. (Characters cannot get into the action of a
first-person account unless they encounter the narrator or unless the
narrator is quoting some other person's story.) The corresponding
graphs tend to have more interesting connectivity properties if we
leave the narrator out by setting |x=1|. For example, there are 87
characters in {\sl David Copperfield\/}; the call
|book("david",0,1,0,0,1,1,0)| produces a graph with 86 vertices, one
for every character except David Copperfield himself.

@ The subroutine call |bi_book(@[@t\<title>@>@],n,x,first_chapter,last_chapter,
in_weight,out_weight,seed)| produces a bipartite graph in which the
vertices of the first part are exactly the same as the vertices of the
graph returned by |book|, while the vertices of the second part are
the selected chapters. For example,
$|bi_book|(|"anna"|,\allowbreak 50,0,10,120,1,1,0)$
creates a bipartite graph with $50+111$ vertices. There is an edge between
each character and the chapters in which that character appears.

@ Chapter numbering needs further explanation. {\sl Anna Karenina\/}
has 239 chapters, which are numbered 1.1 through 8.19 in the
work itself but renumbered 1 through 239 as far as the |book| routine
is concerned. Thus, setting |first_chapter=10| and |last_chapter=120|
turns out to be equivalent to selecting chapters 1.10 through 4.19
(more precisely, chapter~10 of book~1 through chapter~19 of book~4).
{\sl Les Mis\'erables\/} has an even more involved scheme; its
356 chapters range from 1.1.1 (part~1, book~1, chapter~1) to
5.9.6 (part~5, book~9, chapter~6). After |book| or |bi_book| has created
a graph, the external integer variable |chapters| will contain the total
number of chapters, and |chap_name| will be an array of strings
containing the structured chapter numbers. For example, after
|book("jean",@[@t\dots@>@])|, we will have |chapters=356|,
|chap_name[1]="1.1.1"|, \dots, |chap_name[356]="5.9.6"|;
|chap_name[0]| will be~|""|.

@d MAX_CHAPS 360 /* no book will have this many chapters */

@<External variables@>=
long chapters; /* the total number of chapters in the selected book */
char *chap_name[MAX_CHAPS]={""}; /* string names of those chapters */

@ As usual, we put declarations of the external variables into the header file
for users to {\bf include}.

@(gb_books.h@>=
extern long chapters; /* the total number of chapters in the selected book */
extern char *chap_name[]; /* string names of those chapters */

@ If the |book| or |bi_book| routine encounters a problem, it
returns |NULL| (\.{NULL}),
after putting a code number into the external variable
|panic_code|. This code number identifies the type of failure.
Otherwise |book| returns a pointer to the newly created graph, which
will be represented with the data structures explained in {\sc GB\_\,GRAPH}.
(The external variable |panic_code| is itself defined in {\sc GB\_\,GRAPH}.)

@d panic(c) @+{@+panic_code=c;@+gb_trouble_code=0;@+return NULL;@+}
@#
@f node long /* the \&{node} type is defined below */

@ The \CEE/ file \.{gb\_books.c} has the overall shape shown here.
It makes use of an internal subroutine
called |bgraph|, which combines the work of |book| and |bi_book|.

@p
#include "gb_io.h" /* we will use the {\sc GB\_\,IO} routines for input */
#include "gb_flip.h" /* we will use the {\sc GB\_\,FLIP} routines
                        for random numbers */
#include "gb_graph.h" /* we will use the {\sc GB\_\,GRAPH} data structures */
#include "gb_sort.h" /* and the |gb_linksort| routine */
@h@#
@<Type declarations@>@;
@<Private variables@>@;
@<External variables@>@;
@#
static Graph *bgraph(bipartite,
    title,n,x,first_chapter,last_chapter,in_weight,out_weight,seed)
  long bipartite; /* should we make the graph bipartite? */
  char *title; /* identification of the selected book */
  unsigned long n; /* number of vertices desired before exclusion */
  unsigned long x; /* number of vertices to exclude */
  unsigned long first_chapter, last_chapter;
    /* interval of chapters leading to edges */
  long in_weight; /* weight coefficient pertaining to chapters
                          in that interval */
  long out_weight; /* weight coefficient pertaining to chapters
                          not in that interval */
  long seed; /* random number seed */
{@+@<Local variables@>@;@#
  gb_init_rand(seed);
  @<Check that the parameters are valid@>;
  @<Skim the data file, recording the characters and computing their
    statistics@>;
  @<Choose the vertices and put them into an empty graph@>;
  @<Read the data file more carefully and fill the graph as instructed@>;
  if (gb_trouble_code) {
    gb_recycle(new_graph);
    panic(alloc_fault); /* (expletive deleted)
                     we ran out of memory somewhere back there */
  }
  return new_graph;
}
@#
Graph *book(title,n,x,first_chapter,last_chapter,in_weight,out_weight,seed)
  char *title;
  unsigned long n, x, first_chapter, last_chapter;
  long in_weight,out_weight,seed;
{@+return bgraph(0L,title,n,x,first_chapter,last_chapter,
  in_weight,out_weight,seed);@+}
Graph *bi_book(title,n,x,first_chapter,last_chapter,in_weight,out_weight,seed)
  char *title;
  unsigned long n, x, first_chapter, last_chapter;
  long in_weight,out_weight,seed;
{@+return bgraph(1L,title,n,x,first_chapter,last_chapter,
    in_weight,out_weight,seed);@+}

@ @<Local var...@>=
Graph *new_graph; /* the graph constructed by |book| or |bi_book| */
register long j,k; /* all-purpose indices */
long characters; /* the total number of characters in the selected book */
register node *p; /* information about the current character */

@ @d MAX_CHARS 600 /* there won't be more characters than this */

@<Check that the parameters are valid@>=
if (n==0) n=MAX_CHARS;
if (first_chapter==0) first_chapter=1;
if (last_chapter==0) last_chapter=MAX_CHAPS;
if (in_weight>1000000 || in_weight<-1000000 ||
     out_weight>1000000 || out_weight<-1000000)
  panic(bad_specs); /* the magnitude of at least one weight is too big */
sprintf(file_name,"%.6s.dat",title);
if (gb_open(file_name)!=0)
  panic(early_data_fault); /* couldn't open the file; |io_errors| tells why */

@ @<Priv...@>=
static char file_name[]="xxxxxx.dat";

@*Vertices.
Each character in a book has been given a two-letter code name for
internal use. The code names are explained at the beginning of each
data file by a number of lines that look like this:
$$\hbox{\tt XX \<name>,\<description>}$$
For example, here's one of the lines near the beginning of |"anna.dat"|:
$$\hbox{\tt AL Alexey Alexandrovitch Karenin, minister of state}$$
The \<name> does not contain a comma; the \<description> might.

A blank line follows the cast of characters.

Internally, we will think of the two-letter code as a radix-36 integer.
Thus \.{AA} will be the number $10\times36+10$, and \.{ZZ} will be
$35\times36+35$. The |gb_number| routine in {\sc GB\_\,IO} is set up to
input radix-36 integers just as it does hexadecimal ones.
In {\sl The Iliad}, many of the minor characters have numeric digits
in their code names because the total number of characters is too
large to permit mnemonic codes for everybody.

@d MAX_CODE 1296 /* $36\times36$, the number of two-digit codes in radix 36 */

@ In order to choose the vertices, we want to represent each character
as a node whose key corresponds to its weight; then the |gb_linksort|
routine of {\sc GB\_\,SORT} will provide the desired rank-ordering. We will
find it convenient to use these nodes for all the data processing that
|bgraph| has to do.

@<Type dec...@>=
typedef struct node_struct { /* records to be sorted by |gb_linksort| */
  long key; /* the nonnegative sort key (weight plus $2^{30}$) */
  struct node_struct *link; /* pointer to next record */
  long code; /* code number of this character */
  long in; /* number of occurrences in selected chapters */
  long out; /* number of occurrences in unselected chapters */
  long chap; /* seen most recently in this chapter */
  Vertex *vert; /* vertex corresponding to this character */
} node;

@ Not only do nodes point to codes, we also want codes to point to nodes.

@<Priv...@>=
static node node_block[MAX_CHARS]; /* array of nodes for working storage */
static node *xnode[MAX_CODE]; /* the node, if any, having a given code */

@ We will read the data file twice, once quickly (to collect statistics)
and once more thoroughly (to record detailed information). Here is the
quick version.

@<Skim the data file, recording the characters...@>=
@<Read the character codes at the beginning of the data file, and
  prepare a node for each one@>;
@<Skim the chapter information, counting the number of chapters in
  which each character appears@>;
if (gb_close()!=0)
  panic(late_data_fault);
    /* checksum or other failure in data file; see |io_errors| */

@ @<Read the character codes...@>=
for (k=0;k<MAX_CODE;k++) xnode[k]=NULL;
{@+register long c; /* current code entering the system */
  p=node_block; /* current node entering the system */
  while ((c=gb_number(36))!=0) { /* note that \.{00} is not a legal code */
    if (c>=MAX_CODE || gb_char()!=' ') panic(syntax_error);
                                     /* unreadable line in data file */
    if (p>=&node_block[MAX_CHARS])
      panic(syntax_error+1); /* data has too many characters */
    p->link=(p==node_block?NULL:p-1);
    p->code=c;
    xnode[c]=p;
    p->in=p->out=p->chap=0;
    p->vert=NULL;
    p++;
    gb_newline();
  }
  characters=p-node_block;
  gb_newline(); /* bypass the blank line that terminates the character data */
}

@ Later we will read through this part of the file again, extracting
additional information if it turns out to be relevant. The
\<description> string is provided to users in a |desc| field,
in case anybody cares to look at it. The |in| and |out| statistics
are also made available in utility fields called |in_count| and |out_count|.
The code value is placed in the |short_code| field.

@d desc z.S /* utility field |z| points to the \<description> string */
@d in_count y.I /* utility field |y| counts appearances in selected chapters */
@d out_count x.I /* utility field |x| counts appearances in other chapters */
@d short_code u.I /* utility field |u| contains a radix-36 number */

@<Read the data about characters again, noting vertex names and the
  associated descriptions@>=
{@+register long c; /* current code entering the system a second time */
  while ((c=gb_number(36))!=0) {@+register Vertex *v=xnode[c]->vert;
    if (v) {
      if (gb_char()!=' ') panic(impossible); /* can't happen */
      gb_string(str_buf,','); /* scan the \<name> part */
      v->name=gb_save_string(str_buf);
      if (gb_char()!=',')
        panic(syntax_error+2); /* missing comma after \<name> */
      if (gb_char()!=' ')
        panic(syntax_error+3); /* missing space after comma */
      gb_string(str_buf,'\n'); /* scan the \<description> part */
      v->desc=gb_save_string(str_buf);
      v->in_count=xnode[c]->in;
      v->out_count=xnode[c]->out;
      v->short_code=c;
    }
    gb_newline();
  }
  gb_newline(); /* bypass the blank line that terminates the character data */
}  

@ @(gb_books.h@>=
#define desc @t\quad@> z.S /* utility field definitions for the header file */
#define in_count @t\quad@> y.I
#define out_count @t\quad@> x.I
#define short_code @t\quad@> u.I

@*Edges.
The second part of the data file has a line for each chapter, containing
``cliques of encounters.'' For example, the line
$$\hbox{\tt3.22:AA,BB,CC,DD;CC,DD,EE;AA,FF}$$
means that, in chapter 22 of book 3, there were encounters between the pairs
$$\def\\{{\rm,} }
\hbox{\tt AA-BB\\AA-CC\\AA-DD\\BB-CC\\BB-DD\\CC-DD\\CC-EE\\DD-EE\\{\rm and }%
AA-FF\rm.}$$
(The encounter \.{CC-DD} is specified twice, once in the clique
\.{AA,BB,CC,DD} and once in \.{CC,DD,EE}; this does not imply anything about
the actual number of encounters between \.{CC} and \.{DD} in the chapter.)

A clique might involve one character only, when that character is featured
in sort of a soliloquy.

A chapter might contain no references to characters at all. In such a case
the `\.:' following the chapter number is omitted.

There might be more encounters than will fit on a single line. In such cases,
continuation lines begin with `\.{\&:}'. This convention turns out to be
needed only in \.{homer.dat}; chapters in {\sl The Iliad\/} are
substantially more complex than the chapters in other GraphBase books.

On our first pass over the data, we simply want to compute statistics about
who appears in what chapters, so we ignore the distinction between
commas and semicolons.

@<Skim the chapter information, counting the number of chapters in
  which each character appears@>=
for (k=1; k<MAX_CHAPS && !gb_eof(); k++) {
  gb_string(str_buf,':'); /* read past the chapter number */
  if (str_buf[0]=='&') k--; /* continuation of previous chapter */
  while (gb_char()!='\n') {@+register long c=gb_number(36);
    if (c>=MAX_CODE)
      panic(syntax_error+4); /* missing punctuation between characters */
    p=xnode[c];
    if (p==NULL) panic(syntax_error+5); /* unknown character */
    if (p->chap!=k) {
      p->chap=k;
      if (k>=first_chapter && k<=last_chapter) p->in++;
      else p->out++;
    }
  }
  gb_newline();
}
if (k==MAX_CHAPS) panic(syntax_error+6); /* too many chapters */
chapters=k-1;

@ Our second pass over the data is very similar to the first, if we
are simply computing a bipartite graph. In that case we add an edge
to the graph between each selected chapter and each selected character
in that chapter. Local variable |chap_base| will point to a
vertex such that |chap_base+k| is the vertex corresponding to chapter~|k|.

The |in_count| of a chapter vertex is the degree of that vertex, i.e., the
number of selected characters that appear in the corresponding chapter.
The |out_count| is the number of characters that appear in the
chapter but were omitted from the graph. Thus the |in_count| and
|out_count| for chapters are analogous to the |in_count| and |out_count|
for characters.

@<Read the chapter information a second time and create the
  appropriate bipartite edges@>=
{
  for (p=node_block;p<node_block+characters;p++) p->chap=0;
  for (k=1; !gb_eof(); k++) {
    gb_string(str_buf,':'); /* read the chapter number */
    if (str_buf[0]=='&') k--;
    else chap_name[k]=gb_save_string(str_buf);
    if (k>=first_chapter && k<=last_chapter) {@+register Vertex *u=chap_base+k;
      if (str_buf[0]!='&') {
        u->name=chap_name[k];
        u->desc=null_string;
        u->in_count=u->out_count=0;
      }
      while (gb_char()!='\n') {@+register long c=gb_number(36);
        p=xnode[c];
        if (p->chap!=k) {@+register Vertex *v=p->vert;
          p->chap=k;
          if (v) {@+
            gb_new_edge(v,u,1L);
            u->in_count++;
          }@+else u->out_count++;
        }
      }
    }
    gb_newline();
  }
}

@ @<Local variables@>=
Vertex *chap_base;
  /* the bipartite vertex for chapter~|k| is |chap_base+k| */

@ The second pass has to work a little harder when we are recording
encounters from cliques, but the logic isn't difficult really.
We insert a reference to the first chapter that generated each edge, in
utility field |chap_no| of the corresponding |Arc| record.

@d chap_no a.I /* utility field |a| holds a chapter number */

@<Read the chapter information a second time and create the
  appropriate edges for encounters@>=
for (k=1; !gb_eof(); k++) {@+char *s;
  s=gb_string(str_buf,':'); /* read the chapter number */
  if (str_buf[0]=='&') k--;
  else {@+if (*(s-2)=='\n') *(s-2)='\0';
    chap_name[k]=gb_save_string(str_buf);
  }
  if (k>=first_chapter && k<=last_chapter) {@+register long c=gb_char();
    while (c!='\n') {@+register Vertex **pp=clique_table;
      register Vertex **qq,**rr; /* pointers within the clique table */
      do@+{@+
        c=gb_number(36); /* set |c| to code for next character of clique */
        if (xnode[c]->vert) /* is that character a selected vertex? */
          *pp++=xnode[c]->vert;
            /* if so, that vertex joins the current clique */
        c=gb_char();
      }@+while (c==','); /* repeat until end of the clique */
      for (qq=clique_table;qq+1<pp;qq++)
        for (rr=qq+1;rr<pp;rr++)
          @<Make the vertices |*qq| and |*rr| adjacent,
              if they aren't already@>;
    }
  }
  gb_newline();
}

@ @(gb_books.h@>=
#define chap_no @[a.I@] /* utility field definition in the header file */

@ @<Priv...@>=
static Vertex *clique_table[30];
 /* pointers to vertices in the current clique */

@ @<Make the vertices |*qq| and |*rr| adjacent...@>=
{@+register Vertex *u=*qq, *v=*rr;
  register Arc *a;
  for (a=u->arcs; a; a=a->next)
    if (a->tip==v) goto found;
  gb_new_edge(u,v,1L); /* not found, so they weren't already adjacent */
  if (u<v) a=u->arcs;
  else a=v->arcs; /* the new edge consists of arcs |a| and |a+1| */
  a->chap_no=(a+1)->chap_no=k;
found:;
}

@*Administration.
The program is now complete except for a few missing organizational details.
I will add these after lunch.
@^out to lunch@>

@ OK, I'm back; what needs to be done? The main thing is to create
the graph itself.

@<Choose the vertices and put them into an empty graph@>=
if (n>characters) n=characters;
if (x>n) x=n;
if (last_chapter>chapters) last_chapter=chapters;
if (first_chapter>last_chapter) first_chapter=last_chapter+1;
new_graph=gb_new_graph(n-x+(bipartite?last_chapter-first_chapter+1:0));
if (new_graph==NULL) panic(no_room); /* out of memory already */
strcpy(new_graph->util_types,"IZZIISIZZZZZZZ");
              /* declare the types of utility fields */
sprintf(new_graph->id,"%sbook(\"%s\",%lu,%lu,%lu,%lu,%ld,%ld,%ld)",
  bipartite?"bi_":"",title,n,x,first_chapter,last_chapter,
  in_weight,out_weight,seed);
if (bipartite) {
  mark_bipartite(new_graph,n-x);
  chap_base=new_graph->vertices+(new_graph->n_1-first_chapter);
}
@<Compute the weights and assign vertices to chosen nodes@>;

@ @<Compute the weights and assign vertices to chosen nodes@>=
for (p=node_block; p<node_block+characters; p++)
  p->key=in_weight*(p->in)+out_weight*(p->out)+0x40000000;
gb_linksort(node_block+characters-1);
k=n; /* we will look at this many nodes */
{@+register Vertex *v=new_graph->vertices; /* the next vertex to define */
  for (j=127; j>=0; j--)
    for (p=(node*)gb_sorted[j]; p; p=p->link) {
      if (x>0) x--; /* ignore this node */
      else p->vert=v++; /* choose this node */
      if (--k==0) goto done;
    }
}
done:;

@ Once the graph is there, we're ready to fill it in.

@<Read the data file more carefully and fill the graph as instructed@>=
if (gb_open(file_name)!=0)
  panic(impossible+1);
    /* this can't happen, because we were successful before */
@<Read the data about characters again, noting vertex names and the
  associated descriptions@>;
if (bipartite)
  @<Read the chapter information a second time and create the
    appropriate bipartite edges@>@;
else @<Read the chapter information a second time and create the
  appropriate edges for encounters@>;
if (gb_close()!=0)
  panic(impossible+2); /* again, can hardly happen the second time around */

@* Index. As usual, we close with an index that
shows where the identifiers of \\{gb\_books} are defined and used.