//gradient descent
#define n 2
#include <stdio.h>
#include <math.h>
#include <stdlib.h>


double f(double *x)
{
	double out = 0;

	for (int i = 0; i < n; i++)
	{
		out += (x[i] - 2)*(x[i] - 2);
	}
	return out;
}

void grad(double* x, double *g)
{
	for (int i = 0; i < n; i++)
	{
		g[i] = 2 * x[i] - 4;
	}
}

double dist(double* x1, double* x2)
{
	double d = 0;
	for (int i = 0; i < n; i++)
	{
		d += (x1[i] - x2[i])*(x1[i] - x2[i]);
	}
	return sqrt(d);
}

int descent(double alpha, int pasi, double* x)
{
	double g[n] = { 0,0 };
	for (int i = 0; i < pasi; i++)
	{
		grad(x, g);
		printf("gradient: %lf %lf \n", g[0], g[1]);
		for (int j = 0; j < n; j++)
		{
			x[j] -= alpha*g[j];
		}
		printf("pas: %d x: %lf %lf f: %lf \n", i, x[0], x[1], f(x));
	}
	return pasi;
}

int descent2(double alpha, double eps, double * x)
{
	double g[n] = { 0,0 };
	double old[n];
	double d = 999;
	int pasi = 0;
	while (d > eps)
	{
		for (int j = 0; j < n; j++)
		{
			old[j] = x[j];
		}
		pasi++;
		grad(x, g);
		printf("gradient: %lf %lf \n", g[0], g[1]);
		for (int j = 0; j < n; j++)
		{
			x[j] -= alpha*g[j];
		}
		printf("pas: %d x: %lf %lf f: %lf \n", pasi, x[0], x[1], f(x));
		d = dist(old, x);
	}
	return pasi;
}

int main()
{
	double x[] = { -3, 5 };
	double y[] = { 5, 8 };
	descent(0.3, 10, x);
	descent2(0.3, 0.01, y);
	system("pause");
	return 0;
}