ludcmp.c

快速傅立叶变换程序代码,学信号的同学,可要注意了

#include <math.h>

#define TINY 1.0e-20;

int ludcmp(float **a,int n,int *indx,float *d)
{
  int i,imax=0,j,k,status=0;
  float big,dum,sum,temp;
  float *vv; /* ,*vector();  void nrerror(),free_vector(); */
  
  vv=vector(1,n);
  *d=1.0;
  for (i=1;i<=n;i++) {
    big=0.0;
    for (j=1;j<=n;j++)
      if ((temp=fabs(a[i][j])) > big) big=temp;
    if (big == 0.0) {
      fprintf( stderr , "Singular matrix in routine LUDCMP\n");
      status -- ;
      return (status) ; 
    }
    vv[i]=1.0/big;
	}
  for (j=1;j<=n;j++) {
    for (i=1;i<j;i++) {
      sum=a[i][j];
      for (k=1;k<i;k++) sum -= a[i][k]*a[k][j];
      a[i][j]=sum;
    }
    big=0.0;
    for (i=j;i<=n;i++) {
      sum=a[i][j];
      for (k=1;k<j;k++)
	sum -= a[i][k]*a[k][j];
      a[i][j]=sum;
      if ( (dum=vv[i]*fabs(sum)) >= big) {
	big=dum;
	imax=i;
      }
    }
    if (j != imax) {
      for (k=1;k<=n;k++) {
	dum=a[imax][k];
	a[imax][k]=a[j][k];
	a[j][k]=dum;
      }
      *d = -(*d);
      vv[imax]=vv[j];
    }
    indx[j]=imax;
    if (a[j][j] == 0.0) a[j][j]=TINY;
    if (j != n) {
      dum=1.0/(a[j][j]);
      for (i=j+1;i<=n;i++) a[i][j] *= dum;
    }
  }
  free_vector(vv,1,n);
  return ( status ) ; 
}

#undef TINY