d4r4.cpp

数值计算c++源代码,包括各种算法。很有用的。

#include <iostream.h>
#include <math.h>
#include <iomanip.h>
#include <stdlib.h>
#include <fstream.h>
#include <string>

double gammln(double xx)
{
	int j;
	float temp;
    double cof[6],stp,half,one,fpf,x,tmp,ser;
    cof[1] = 76.18009173;
    cof[2] = -86.50532033;
    cof[3] = 24.01409822;
    cof[4] = -1.231739516;
    cof[5] = 0.00120858003;
    cof[6] = -0.00000536382;
    stp = 2.50662827465;
    half = 0.5;
    one = 1.0;
    fpf = 5.5;
    x = xx - one;
    tmp = x + fpf;
    tmp = (x + half) * log(tmp) - tmp;
    ser = one;
    for (j = 1;j<=6;j++)
	{
        x = x + one;
        ser = ser + cof[j] / x;
    }
    temp = tmp + log(stp * ser);
	return temp;
}

double factln(int n)
{
	int i;
    double a[101],temp;
    for( i = 1;i<=100;i++)
        a[i] = -1.0;
    if (n < 0)
	{
        cout<<"negative factorial";
        exit(1);
	}
    if (n <= 99)
	{
        if( a[n + 1] < 0.0)  a[n + 1] = gammln(n + 1.0);
        temp = a[n + 1];
	}
    else
        temp = gammln(n + 1.0);
	return temp;
}

void main()
{
    //program d4r4
    //driver for routine factln
    int i,x;
	char text[20];
    double nval,actual; 
    const double pi = 3.1415926;
    fstream fin;
    fin.open("d:\\vc常用数值算法集\\data\\fncval.dat",ios::in);
    while (strcmp(text,"N-factorial")!=0)
	{
      fin>>text;
	}
    fin>>nval; 
    cout<<text<<" "<<endl;
    fin>>text;
    cout<<endl;
    cout<<"    x        Actual           facval(n)"<<endl;
    for( i = 1; i<=nval; i++)
	{
        fin>>x;
		fin>>actual;           
		cout<<setw(3)<<x;
		cout<<setprecision(8)<<setw(18)<<log(actual);
		cout<<setprecision(8)<<setw(18)<<factln(x)<<endl;			
    }
}