0

到目前为止，这是我的代码。因为我一直得到一个不正确的答案，所以似乎有什么问题。我正在写一个格式化的文本文件：2 3.0 1.0

2 是数组的大小，然后 3.0 和 1.0 是系数。希望我的解释没有遗漏太多。任何帮助将不胜感激。谢谢

double polyeval(double* polyarray, double x, int arraySize)
{
    //int result = 0;

    if(arraySize == 0)
    {
        return polyarray[arraySize];
    }

    //result += x*(polyarray[arraySize]+polyeval(polyarray,x,arraySize-1));
      return polyarray[arraySize-1]+ (x* (polyeval(polyarray,x,arraySize-1)));
       //return result;
}

int main ()
{
    int arraySize;
    double x;
    double *polyarray;

    ifstream input;
    input.open("polynomial.txt");
    input >> arraySize;
    polyarray = new double [arraySize];
    for (int a = arraySize - 1; a >= 0; a--)
    {
        input >> polyarray[a];
    }

    cout << "For what value x would you like to evaluate?" << endl;
    cin >> x;
    cout << "Polynomial Evaluation: " << polyeval(polyarray, x, arraySize);

    delete [] polyarray;
}

如果我读入一个大小不同的格式的文本文件，它将解决用户给出的任何值 x 的想法

4

4 回答 4

0

只是胡乱猜测

for (int a = arraySize - 1; a >= 0; a--)
//                            ^^
{
    input >> polyarray[a];
}
于 2013-04-17T04:16:37.427 回答
0

这里有一个错误：

for (int a = arraySize - 1; a > 0; a--)
{                             //^^should be a >=0 
    input >> polyarray[a];
}

您以这种方式缺少一些条目。

递归函数应如下所示：

int polyeval(double* polyarray, double x, int arraySize)
{
   if(arraySize == 1)
   {
      return polyarray[arraySize-1];
   }

   return x*(polyarray[arraySize-1]+polyeval(polyarray,x,arraySize-1));
}
于 2013-04-17T04:16:46.327 回答
0

The problem is mainly with the definition of the polynomial coefficients. Your code assumes a polynomial on the form:

x( p(n) + x( p(n-1) + x( p(n-2) + ... x(p(1) + p(0)))..))

This line:

result += x*(polyarray[arraySize]+polyeval(polyarray,x,arraySize-1));

Should become:

result += pow(x,arraySize)*polyarray[arraySize]+polyeval(polyarray,x,arraySize-1);

This way the polynomial is defined correctly as p(n)x^n + p(n-1)x^(n-1) ... + p1 x + p0

于 2013-04-17T04:37:02.837 回答
0

无法准确计算出您要做什么，或者为什么要使用递归。因此，我创建了一个似乎可以给出正确结果的非递归版本。

#include <iostream>
using namespace std;

double polyeval(const double* polyarray, double x, int arraySize) {
    if(arraySize <= 0) { return 0; }
    double value = 0;
    const double * p = polyarray + (arraySize-1);
    for(int i=0; i<arraySize; ++i) {
        value *= x;
        value += *p;
        p--;
    }
    return value;
}

int main () {

    const int arraySize = 3;

    const double polyarrayA[3] = {0.0,0.0,1.0}; // 0 + 0 x + 1 x^2 
    const double polyarrayB[3] = {0.0,1.0,0.0}; // 0 + 1 x + 0 x^2 
    const double polyarrayC[3] = {1.0,0.0,0.0}; // 1 + 0 x + 0 x^2

    cout << "Polynomial Evaluation A f(x) = " << polyeval(polyarrayA, 0.5, arraySize)<<std::endl;
    cout << "Polynomial Evaluation B f(x) = " << polyeval(polyarrayB, 0.5, arraySize)<<std::endl;    
    cout << "Polynomial Evaluation C f(x) = " << polyeval(polyarrayC, 0.5, arraySize)<<std::endl;    


}

你可以看到它在这里运行：

http://ideone.com/HE4r6x

于 2013-04-17T05:03:08.743 回答