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// Chebyshev Polynomial of the First Kind
//
// chebyshev_t - T_n(x)
//
// T_0 = 1, T_1 = x, T_n = 2x*T_(n-1) - T_(n-2)
//
// Inputs: 2 (x, n)
// Outputs: 1 (T_n(x))
// Constants: 0
#include <math.h>
#include "ts.h"
ts_parameter_t const ts_chebyshev_t_p = { .n_inputs = 2, .n_outputs = 1, .n_constants = 0, .params_size = 0 };
uint_t ts_chebyshev_t_offset( ts_constant_t const *c )
{
( void )c;
return ( 0 );
}
int ts_chebyshev_t(
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_chebyshev_t_p );
(void)c;
for( uint_t i = 0; i < n; ++i )
{
fp_t xv = x[0][i];
uint_t n_val = (uint_t)x[1][i];
if (x[1][i] < 0 || x[1][i] > 10000) { y[0][i] = 0; continue; }
if( n_val == 0 )
{
y[0][i] = 1.0;
}
else if( n_val == 1 )
{
y[0][i] = xv;
}
else
{
fp_t t0 = 1.0;
fp_t t1 = xv;
for( uint_t k = 2; k <= n_val; ++k )
{
fp_t t2 = 2.0 * xv * t1 - t0;
t0 = t1;
t1 = t2;
}
y[0][i] = t1;
}
}
return 0;
}
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