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Unbias a random generator: Difference between revisions
→{{header|C}}
(→{{header|Perl}}: fixed stddev for binomial distr) |
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The actual unbiasing should be done by generating two numbers at a time from randN and only returning a 1 or 0 if they are different. As long as you always return the first number or always return the second number, the probabilities discussed above should take over the biased probability of randN.
=={{header|C}}==
<lang C>#include <stdio.h>
#include <stdlib.h>
int biased(int bias)
{
/* balance out the bins, being pedantic */
int r, rand_max = RAND_MAX - (RAND_MAX % bias);
while ((r = rand()) > rand_max);
return rand() < rand_max / bias;
}
int unbiased(int bias)
{
int a;
while ((a = biased(bias)) == biased(bias));
return a;
}
int main()
{
int b, n = 10000, cb, cu, i;
for (b = 3; b <= 6; b++) {
for (i = cb = cu = 0; i < n; i++) {
cb += biased(b);
cu += unbiased(b);
}
printf("bias %d: %5d %5.3f%% vs %5d %5.3f\n", b,
cb, 100. * cb / n, cu, 100. * cu / n);
}
return 0;
}</lang>output<lang>bias 3: 3309 33.090% vs 4971 49.710
bias 4: 2513 25.130% vs 4943 49.430
bias 5: 1976 19.760% vs 4965 49.650
bias 6: 1674 16.740% vs 5003 50.030</lang>
=={{header|Clojure}}==
<lang Clojure>(defn biased [n]
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