c - 用C语言求解微分方程时错误答案

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我是 C 编程新手，正在编写一个程序来求解简单的微分方程，该方程将输出作为 x 的值。但我没有得到正确的结果。

我得到了正确的方程值，但微分方程的值是错误的。代码编译时没有任何警告或错误。

#include <stdio.h>
#include <conio.h>
#include <math.h>

float poly(float a[], int, float);
float deriv(float a[], int, float);

int main()
{
  float x, a[10], y1, dy1;
  int deg, i;

printf("Enter the degree of polynomial equation: ");
scanf("%d", &deg);

printf("Ehter the value of x for which the equation is to be evaluated: ");
scanf("%f", &x);

for(i=0;i<=deg;i++)
{
    printf("Enter the coefficient of x to the power %d: ",i);
    scanf("%f",&a[i]);
}

y1 = poly(a, deg, x);
dy1 = deriv(a, deg, x);

printf("The value of polynomial equation for the value of x = %.2f is: %.2f",x,y1);
printf("\nThe value of the derivative of the polynomial equation at x = %.2f is: %.2f",x,dy1);

return 0;
 }

 /* function for finding the value of polynomial at some value of x */

 float poly(float a[], int deg, float x)
 {
    float p;
    int i;

p = a[deg];

for(i=deg;i>=1;i--)
{
    p = (a[i-1] + x*p);
}

return p;
}

/* function for finding the derivative at some value of x */
  float deriv(float a[], int deg, float x)
   {
   float d[10], pd = 0, ps;
int i;

for(i=0;i<=deg;i++)
{
    ps = pow(x, deg-(i+1));
    d[i] = (deg-1)*a[deg-1]*ps;
    pd = pd + d[i];
}

return pd;
}

Answer 1

你犯了一个简单的逻辑错误。函数中 float deriv(float a[], int deg, float x) 应该是 d[i] = (deg-i)*a[deg-i]*ps; 。所以你的函数看起来像这样

/* function for finding the derivative at some value of x */
float deriv(float a[], int deg, float x)
{
  float d[10], pd = 0, ps;
  int i;

  for(i=0;i<=deg;i++)
  {
     ps = pow(x, deg-(i+1));
     d[i] = (deg-i)*a[deg-i]*ps;
     pd = pd + d[i];
  }

  return pd;
 }

祝你 future 一切顺利。