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#include <apop.h>
#define Diff(left, right, eps) Apop_stopif(fabs((left)-(right))>(eps), abort(), 0, "%g is too different from %g (abitrary limit=%g).", (double)(left), (double)(right), eps)
long double entropy_base_2(gsl_vector *x) {
return apop_vector_entropy(x)/log(2);
}
int main(){
apop_model *flip = apop_model_set_parameters(apop_bernoulli, .5);
//zero data => entropy zero
gsl_vector *v = gsl_vector_calloc(1);
assert(apop_vector_entropy(v) == 0);
//negative data => NaN
gsl_vector_set(v, 0, -1);
int v1 = apop_opts.verbose;
apop_opts.verbose = -1;
assert(isnan(apop_vector_entropy(v)));
apop_opts.verbose = v1;
//N equiprobable bins => entropy = log(N)
v = apop_vector_realloc(v, 100);
gsl_vector_set_all(v, 1./100);
Diff(log(100), apop_vector_entropy(v), 1e-5);
//Normalization is optional. You may send a vector of counts.
gsl_vector_set_all(v, 1);
Diff(log(100), apop_vector_entropy(v), 1e-5);
//flip two coins.
apop_data *coin_flips = apop_model_draws(flip, .count=10000);
apop_data *c2 = apop_model_draws(flip, .count=10000);
apop_data_stack(c2, coin_flips, 'c', .inplace='y');
//entropy of one coin flip in base2 == 1
apop_data_pmf_compress(coin_flips);
Diff(entropy_base_2(coin_flips->weights), 1, 1e-3);
//entropy of two coin flips in base2 == 2
apop_data_pmf_compress(c2);
Diff(entropy_base_2(c2->weights), 2, 1e-3);
//flip three coins, via model cross products
Diff(entropy_base_2(apop_data_pmf_compress(apop_model_draws(
apop_model_cross(flip, flip, flip) ,.count=10000))->weights), 3, 1e-3);
apop_data_free(coin_flips);
apop_data_free(c2);
gsl_vector_free(v);
}
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