|
6 | 6 | * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group |
7 | 7 | * Portions Copyright (c) 1994, Regents of the University of California |
8 | 8 | * |
9 | | - * $Id: geqo_selection.c,v 1.12 2001/01/24 19:42:57 momjian Exp $ |
| 9 | + * $Id: geqo_selection.c,v 1.12.4.1 2005/06/14 14:21:43 tgl Exp $ |
10 | 10 | * |
11 | 11 | *------------------------------------------------------------------------- |
12 | 12 | */ |
|
43 | 43 |
|
44 | 44 | staticintlinear(intmax,doublebias); |
45 | 45 |
|
46 | | -/* geqo_selection |
47 | | - * |
| 46 | + |
| 47 | +/* |
| 48 | + * geqo_selection |
48 | 49 | * according to bias described by input parameters, |
49 | | - * second genes are selected from the pool |
| 50 | + *first andsecond genes are selected from the pool |
50 | 51 | */ |
51 | 52 | void |
52 | 53 | geqo_selection(Chromosome*momma,Chromosome*daddy,Pool*pool,doublebias) |
53 | 54 | { |
54 | 55 | intfirst, |
55 | 56 | second; |
56 | 57 |
|
57 | | -first=(int)linear(pool->size,bias); |
58 | | -second=(int)linear(pool->size,bias); |
| 58 | +first=linear(pool->size,bias); |
| 59 | +second=linear(pool->size,bias); |
59 | 60 |
|
60 | 61 | if (pool->size>1) |
61 | 62 | { |
62 | 63 | while (first==second) |
63 | | -second=(int)linear(pool->size,bias); |
| 64 | +second=linear(pool->size,bias); |
64 | 65 | } |
65 | 66 |
|
66 | 67 | geqo_copy(momma,&pool->data[first],pool->string_length); |
67 | 68 | geqo_copy(daddy,&pool->data[second],pool->string_length); |
68 | 69 | } |
69 | 70 |
|
70 | | -/* linear |
| 71 | +/* |
| 72 | + * linear |
71 | 73 | * generates random integer between 0 and input max number |
72 | 74 | * using input linear bias |
73 | 75 | * |
74 | 76 | * probability distribution function is: f(x) = bias - 2(bias - 1)x |
75 | 77 | * bias = (prob of first rule) / (prob of middle rule) |
76 | | - * |
77 | 78 | */ |
78 | | - |
79 | 79 | staticint |
80 | 80 | linear(intpool_size,doublebias)/* bias is y-intercept of linear |
81 | 81 | * distribution */ |
82 | 82 | { |
83 | 83 | doubleindex;/* index between 0 and pop_size */ |
84 | 84 | doublemax= (double)pool_size; |
85 | 85 |
|
86 | | -index=max* (bias-sqrt((bias*bias)-4.0* (bias-1.0)*geqo_rand())) |
87 | | -/2.0 / (bias-1.0); |
| 86 | +/* |
| 87 | + * If geqo_rand() returns exactly 1.0 then we will get exactly max from |
| 88 | + * this equation, whereas we need 0 <= index < max. Also it seems possible |
| 89 | + * that roundoff error might deliver values slightly outside the range; |
| 90 | + * in particular avoid passing a value slightly less than 0 to sqrt(). |
| 91 | + * If we get a bad value just try again. |
| 92 | + */ |
| 93 | +do { |
| 94 | +doublesqrtval; |
| 95 | + |
| 96 | +sqrtval= (bias*bias)-4.0* (bias-1.0)*geqo_rand(); |
| 97 | +if (sqrtval>0.0) |
| 98 | +sqrtval=sqrt(sqrtval); |
| 99 | +index=max* (bias-sqrtval) /2.0 / (bias-1.0); |
| 100 | +}while (index<0.0||index >=max); |
88 | 101 |
|
89 | 102 | return (int)index; |
90 | 103 | } |