多项式拟合函数polyfit之C语言的源码

*Functtion :多项式拟合polyfit **********************************************/ #include #include #include #include main() { int i,j,m,n=7,poly_n=2; double x[7]={1,2,3,4,6,7,8},y[7]={2,3,6,7,5,3,2}; double a[3]; void polyfit(int n,double *x,double *y,int poly_n,double a[]); system("cls"); polyfit(n,x,y,poly_n,a); for (i=0;i     printf("a[%d]=%g/n",i,a[i]); getch(); } /*==================polyfit(n,x,y,poly_n,a)===================*/ /*=======拟合y=a0+a1*x+a2*x^2+……+apoly_n*x^poly_n========*/ /*=====n是数据个数 xy是数据值 poly_n是多项式的项数======*/ /*===返回a0,a1,a2,……a[poly_n]，系数比项数多一（常数项）=====*/ void polyfit(int n,double x[],double y[],int poly_n,double a[]) { int i,j; double *tempx,*tempy,*sumxx,*sumxy,*ata; void gauss_solve(int n,double A[],double x[],double b[]); tempx=calloc(n,sizeof(double)); sumxx=calloc(poly_n*2+1,sizeof(double)); tempy=calloc(n,sizeof(double)); sumxy=calloc(poly_n+1,sizeof(double)); ata=calloc((poly_n+1)*(poly_n+1),sizeof(double)); for (i=0;i     {       tempx[i]=1;       tempy[i]=y[i];      } for (i=0;i<2*poly_n+1;i++)      for (sumxx[i]=0,j=0;j   {     sumxx[i]+=tempx[j];     tempx[j]*=x[j];    } for (i=0;i    for (sumxy[i]=0,j=0;j   {     sumxy[i]+=tempy[j];     tempy[j]*=x[j];    } for (i=0;i     for (j=0;jata[i*(poly_n+1)+j]=sumxx[i+j]; gauss_solve(poly_n+1,ata,a,sumxy); free(tempx); free(sumxx); free(tempy); free(sumxy); free(ata); } void gauss_solve(int n,double A[],double x[],double b[]) { int i,j,k,r; double max; for (k=0;k     {       max=fabs(A[k*n+k]); /*find maxmum*/       r=k;       for (i=k+1;i   if (max      {        max=fabs(A[i*n+i]);        r=i;       }       if (r!=k) for (i=0;i      {        max=A[k*n+i];        A[k*n+i]=A[r*n+i];        A[r*n+i]=max;       }       max=b[k];                    /*change array:b[k]&b[r]     */       b[k]=b[r];       b[r]=max;       for (i=k+1;i   {     for (j=k+1;j        A[i*n+j]-=A[i*n+k]*A[k*n+j]/A[k*n+k];     b[i]-=A[i*n+k]*b[k]/A[k*n+k];    }      } for (i=n-1;i>=0;x[i]/=A[i*n+i],i--)      for (j=i+1,x[i]=b[i];jx[i]-=A[i*n+j]*x[j]; }