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// Binomial Coefficient
//
// binomial - C(n, k)
//
// Number of combinations: C(n, k) = n! / (k! * (n-k)!)
//
// Inputs: 2 (n, k)
// Outputs: 1 (coefficient)
// Constants: 0
#include <math.h>
#include "ts.h"
ts_parameter_t const ts_binomial_p = { .n_inputs = 2, .n_outputs = 1, .n_constants = 0, .params_size = 0 };
uint_t ts_binomial_offset( ts_constant_t const *c )
{
( void )c;
return ( 0 );
}
int ts_binomial(
fp_t * const *y, uint_t y_n,
fp_t const * const *x, uint_t x_n,
uint_t n, ts_constant_t const *c
)
{
TS_PROLOGUE( ts_binomial_p );
(void)c;
/* C(n, k) = n! / (k! * (n-k)!) */
for (uint_t i = 0; i < n; ++i)
{
fp_t n_val = floor(x[0][i]);
fp_t k_val = floor(x[1][i]);
if (k_val > n_val || k_val < 0 || n_val < 0)
{
y[0][i] = 0;
continue;
}
/* Use symmetry: C(n,k) = C(n, n-k) */
if (k_val > n_val - k_val)
k_val = n_val - k_val;
fp_t result = 1;
for (uint_t j = 0; j < (uint_t)k_val; ++j)
{
result = result * (n_val - j) / (j + 1);
}
y[0][i] = result;
}
return 0;
}
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