sigmoid.cpp

C++神经网络开发包,基于C++语言

/*
 * public/ann/annfunc/sigmoid.c
 * 2004-05-03 by ShanLanshan
 */
#include "public/ann/annfunc/annfunc.h"
#include "public/ann/annfunc/sigmoid.h"

namespace ann {
namespace annfunc {
namespace sigmoid {

	static bool init();
	static void finalize();
	static ann_float main_func(ann_float f);
	static ann_float derivative_func(ann_float f);
	static ann_float derivative_func2(ann_float f);
	static void multi_main_func(ann_float *src, ann_int len, ann_float *dst);
	static void multi_derivative_func(ann_float *src, ann_int len, ann_float *dst);
	static void multi_derivative_func2(ann_float *src, ann_int len, ann_float *dst);

	extern  AnnFuncGroup g_funcgroup = {
		"sigmoid",
		"双曲正切函数",
		init,
		finalize,
		main_func,
		derivative_func,
		derivative_func2,
		multi_main_func,
		multi_derivative_func,
		multi_derivative_func2
	};

	static bool init()
	{
		return true;
	}

	static void finalize() {}

	/* 
	 * S型函数 
	 * w = 1 / ( 1 + e ^ (-f))
	 */
	static ann_float main_func(ann_float f)
	{
		ann_float u;
		u = pow(E, -f);
		return 1 / (1 + u);
	}

	/* S型函数的导数
	 *
	 * w = 1 / (1 + e ^ -f)
	 * Let u = e ^ -f, Then w = 1 / (1 + u), @u/@f = -u
	 * @w/@u = -1/((1 + u) ^ 2)
	 * @w/@f = @w/@u * @u/@f = u / ((1 + u) ^ 2), u = e ^ -f
	 */
	static ann_float derivative_func(ann_float f)
	{
		ann_float u;
		u = pow(E, -f);
		return u / ((1 + u) * (1 + u));
	}

	/* 
	 * 求双曲正切函数的导数值，输入的参数是主函数的值
	 * 	Let u(f) = e ^ (-f)
	 * 	w = 1 / (1 + u)
	 *	@w/@f = u / ((1 + u) ^ 2)
	 *        = ((1 + u) - 1) / ((1 + u) ^ 2)
	 *        = w * ((1 + u) - 1) / (1 + u)
	 *        = w * (1 - w)
	 */
	static ann_float derivative_func2(ann_float f)
	{
		return f * (1 - f);
	}

	static void multi_main_func(ann_float *src, ann_int len, ann_float *dst)
	{
		ann_float u, f;

		assert(src != NULL);
		if (dst == NULL)
			dst = src;

		for (int i=0; i<len; ++i) {
			f = src[i];
			u = pow(E, -f);
			dst[i] = 1 / (1 + u);
		}
	}
	
	static void multi_derivative_func(ann_float *src, ann_int len, ann_float *dst)
	{
		ann_float u, f;

		assert(src != NULL);
		if (dst == NULL)
			dst = src;

		for (int i=0; i<len; ++i) {
			f = src[i];
			u = pow(E, -f);
			dst[i] = u / ((1 + u) * (1 + u));
		}
	}

	static void multi_derivative_func2(ann_float *src, ann_int len, ann_float *dst)
	{
		ann_float f;

		assert(src != NULL);
		if (dst == NULL)
			dst = src;

		for (int i=0; i<len; ++i) {
			f = src[i];
			dst[i] = f * (1 - f);
		}
	}

}}} // namespace ann::annfunc::sigmoid