lib/center_of_gravity.c


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// Center of Gravity
//
// center_of_gravity - COG
//
// 1 - 2 * SUM(i*x_i) / ((k+1) * SUM(x_i)), oscillates around 0
//
// Inputs:    1
// Outputs:   1 (COG)
// Constants: 1 (period)

#include "ts.h"

typedef struct {
    uint_t k;
} ts_center_of_gravity_params_t;

ts_parameter_t const ts_center_of_gravity_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_center_of_gravity_params_t) };

uint_t ts_center_of_gravity_offset( ts_constant_t const *c )
{
	( void )c;
	return ( c ? ((ts_center_of_gravity_params_t const *)c)->k - 1 : 0 );
}

int ts_center_of_gravity(
	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_center_of_gravity_p );
	if ( !c ) return -1;
	uint_t k = ((ts_center_of_gravity_params_t const *)c)->k;
	if (k == 0 || n < k) return -1;

	for( uint_t i = k - 1; i < n; ++i )
	{
		fp_t sum_ix = 0;
		fp_t sum_x = 0;
		for( uint_t j = 0; j < k; ++j )
		{
			fp_t idx = (fp_t)(j + 1);
			fp_t val = x[0][i - k + 1 + j];
			sum_ix += idx * val;
			sum_x += val;
		}
		if( sum_x == 0 )
			y[0][i] = 0;
		else
			y[0][i] = 1.0 - 2.0 * sum_ix / ( ( (fp_t)k + 1.0 ) * sum_x );
	}
	return 0;
}