我对 C 编程非常陌生。我正在使用“C 中的数字食谱”一书中的 C 代码进行多项式回归，但我在实现/编译它时遇到了问题。
这是我正在使用的代码。一些//显示我尝试将程序更改为 C++。如果我不能让它在 C 下构建，也许它可以在 C++ 下工作？
我已将其添加int main()到程序中以实现它。nrutil.h是头文件，但我没有使用它，因为我将所需的函数转移到了 .ccp 文件（函数matrix(), vector(), nrerror(), SQR()）。
我使用的编译器是 MSVC 2010 Express。
//#include "nrutil.h"
#include <stdio.h>
//#include <iostream>
//using namespace std;
static float sqrarg;
#define SQR(a) ((sqrarg=(a)) == 0.0 ? 0.0 : sqrarg*sqrarg)
void nrerror(char error_text[]);
float *vector(long nl, long nh);
float **matrix(long nrl, long nrh, long ncl, long nch);
int fpoly(float x, float a[], int ma){
int j;
a[1]=1.0;
for(j=2; j<=ma;j++)
a[j]=a[j-1]*x;
return ma;
}
void lfit( float x[], float y[], float sig[], int ndat, float a[], int ia[], int ma, float **covar, float *chisq)
//Given a set of data points x[1..ndat], y[1..ndat] with individual standard deviations
//sig[1..ndat], use χ2 minimization to fit for some or all of the coefficients a[1..ma] of
//a function that depends linearly on a, y =sum(i)( ai × afunci(x)). The input array ia[1..ma]
//indicates by nonzero entries those components of a that should be fitted for, and by zero entries
//those components that should be held fixed at their input values. The program returns values
//for a[1..ma], χ2 = chisq, and the covariance matrix covar[1..ma][1..ma]. (Parameters
//held fixed will return zero covariances.)Th e user supplies a routine funcs(x,afunc,ma) that
//returns the ma basis functions evaluated at x = x in the array afunc[1..ma].
{
void gaussj(float **a, int n, float **b, int m);
int i,j,k,l,m,mfit=0;
float ym,wt,sum,sig2i,**beta, *afunc;
//vector<float> afunc(1,ma);
//matrix<float> beta(1,ma,1,1);
afunc=vector(1,ma);
beta=matrix(1,ma,1,1);
for (j=1;j<=ma;j++)
if (ia[j]) mfit++;
if (mfit == 0)
nrerror("lfit: no parameters to be fitted");
for (j=1;j<=mfit;j++) { //Initialize the (symmetric)matrix.
for (k=1;k<=mfit;k++) covar[j][k]=0.0;
beta[j][1]=0.0;
}
for (i=1;i<=ndat;i++) { //Loop over data to accumulate coefficients of the normal equations.
fpoly(x[i], afunc ,ma);
ym=y[i];
if (mfit < ma) { //Subtract off dependences on known pieces of the fitting function.
for (j=1;j<=ma;j++)
if (!ia[j]) ym -= a[j]*afunc[j];
}
sig2i=1.0/SQR(sig[i]);
for (j=0,l=1;l<=ma;l++) {
if (ia[l]) {
wt=afunc[l]*sig2i;
for (j++,k=0,m=1;m<=l;m++)
if (ia[m]) covar[j][++k] += wt*afunc[m];
beta[j][1] += ym*wt;
}
}
}
for (j=2;j<=mfit;j++) //Fill in above the diagonal from symmetry.
for (k=1;k<j;k++)
covar[k][j]=covar[j][k];
gaussj(covar,mfit,beta,1); //Matrix solution.
for (j=0,l=1;l<=ma;l++)
if (ia[l]) a[l]=beta[++j][1]; //Partition solution to appropriate coefficients a Evaluate χ2 of the fit.
*chisq=0.0;
for (i=1;i<=ndat;i++) {
fpoly(x[i], afunc,ma);
for (sum=0.0,j=1;j<=ma;j++)
sum += a[j]*afunc[j];
*chisq += SQR((y[i]-sum)/sig[i]);
}
//covsrt(covar,ma,ia,mfit); //Sort covariance matrix to true order of fitting coefficients.
//free_vector(afunc,1,ma);
//free_matrix(beta,1,ma,1,1);
}
//#endif // INTERPFUNCTIONS_H_INCLUDED
int main()
{
float x1[]={100.000000f,88.00000f,76.199997f,68.599998f,54.500000f,37.599998f,26.500000f,17.000000f,8.300000f,0.900000f,-7.200000f,-17.000000f,-24.900000f,-33.799999f,-42.500000f,-51.000000f,-60.500000f,-69.500000f,-75.300003f,-83.099998f,-94.099998f,-103.000000f,-110.099998f};
float y1[]={-2.876821f,-2.788704f,-2.596228f,-2.468143f,-1.898085f,-1.296223f,-0.664981f,-0.245603f,-0.280993f,-0.094657f,-0.184912f,-0.263328f,-0.181819f,-0.132037f,-0.029368f,0.134307f,0.257734f,0.305223f,0.091159f,0.063768f,-0.163334f,-0.136314f,-0.372106f};
float sig1[]={62.2940f,1.0532f};
float a1[]={1.8f,1.6f,1.7f,1.3f};
float **covar1, xa;
int ia1[]={2,3,4,2};
int ma=4, ndat=23;
float *chisq1;
*chisq1=0.9f;
covar1[4][4]=0.0f;
fpoly(xa,a1,ma);
lfit(x1,y1,sig1,ndat,a1,ia1,ma,covar1,chisq1);
}
当我尝试编译这个程序时，它显示了这个错误输出：
1>------ Build started: Project: lfit, Configuration: Debug Win32 ------
1> lfit.cpp
1>c:\users\sony\documents\visual studio 2010\projects\lfit\lfit\lfit.cpp(68): warning C4244: '=' : conversion from 'double' to 'float', possible loss of data
1>c:\users\sony\documents\visual studio 2010\projects\lfit\lfit\lfit.cpp(89): warning C4244: '+=' : conversion from 'double' to 'float', possible loss of data
1>c:\users\sony\documents\visual studio 2010\projects\lfit\lfit\lfit.cpp(110): warning C4700: uninitialized local variable 'chisq1' used
1>c:\users\sony\documents\visual studio 2010\projects\lfit\lfit\lfit.cpp(111): warning C4700: uninitialized local variable 'covar1' used
1>c:\users\sony\documents\visual studio 2010\projects\lfit\lfit\lfit.cpp(113): warning C4700: uninitialized local variable 'xa' used
1>lfit.obj : error LNK2019: unresolved external symbol "void __cdecl gaussj(float * *,int,float * *,int)" (?gaussj@@YAXPAPAMH0H@Z) referenced in function "void __cdecl lfit(float * const,float * const,float * const,int,float * const,int * const,int,float * *,float *)" (?lfit@@YAXQAM00H0QAHHPAPAMPAM@Z)
1>lfit.obj : error LNK2019: unresolved external symbol "void __cdecl nrerror(char * const)" (?nrerror@@YAXQAD@Z) referenced in function "void __cdecl lfit(float * const,float * const,float * const,int,float * const,int * const,int,float * *,float *)" (?lfit@@YAXQAM00H0QAHHPAPAMPAM@Z)
1>lfit.obj : error LNK2019: unresolved external symbol "float * * __cdecl matrix(long,long,long,long)" (?matrix@@YAPAPAMJJJJ@Z) referenced in function "void __cdecl lfit(float * const,float * const,float * const,int,float * const,int * const,int,float * *,float *)" (?lfit@@YAXQAM00H0QAHHPAPAMPAM@Z)
1>lfit.obj : error LNK2019: unresolved external symbol "float * __cdecl vector(long,long)" (?vector@@YAPAMJJ@Z) referenced in function "void __cdecl lfit(float * const,float * const,float * const,int,float * const,int * const,int,float * *,float *)" (?lfit@@YAXQAM00H0QAHHPAPAMPAM@Z)
1>C:\Users\Sony\Documents\Visual Studio 2010\Projects\lfit\Debug\lfit.exe : fatal error LNK1120: 4 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========