12.数据结构之梯度下降查找抛物线的极值

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <iostream>
#include <string.h>

using namespace std;


//计算f(x)=ax^2+bx+c的极值
double gradientDesc(double a, double b, double c, int cnt)
{
	double l = 0.1,fx;
	double x = rand() / (double)RAND_MAX * 20 - 10;
	int i;
	for (int i = 0; i < cnt; i++)
	{
		//f(x)对x求导 f'x(x)=2ax+b
		double gradient = 2 * a * x + b;
		if (a > 0) x = x - gradient * l;
		else x = x + gradient * l;

		//计算f(x)
		 fx= a * x * x + b * x + c;
		printf("i=%d x=%lf fx=%lf gradient=%lf\n", i, x, fx, gradient);
		
	}
	return fx;
}




int main()
{
	srand(time(0));

	int a = rand() % 20 - 10;
	int c = rand() % 20 - 10;
	int b = rand() % 20 - 10;
	a = a == 0 ? 1 : a;

	printf("f(x)=%d^2+%d+%d\n", a, b, c);
	double value=gradientDesc(a, b, c, 100);
	printf("\n\n极值点横坐标为x=%lf\n", value);


	return 0;
}
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