这是fft的程序
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define N 1000
typedef struct
{
double real;
double img;
} complex;void fft(); //快速傅里叶变换
void initw();
void change();void add(complex,complex,complex *);
void mul(complex,complex,complex *);
void sub(complex,complex,complex *);
void output();complex x(N),*w;
int size_x=0;
double PI;int main()
{
int i,method;
void fft();
void initw();
void change();
void add(complex,complex,complex *);
void mul(complex,complex,complex *);
void sub(complex,complex,complex *);
void divi(complex,complex,complex *); PI=atan(1)*4;
printf("please input the size of x:\n");
scanf("%d",&size_x);
printf("please input the date in x(N):\n");
for(i=0;i<size_x;i++)
scanf("%lf%lf",&x[i].real,&x[i].img);
initw();
output();
return 0;
}void fft()
{
int i=0,j=0,k=0,l=0;
complex up,down,product;
change();
for(i=0;i<log(size_x)/log(2);i++)
{
l=1<<i;
for(j=0;j<size_x;j+=2*l)
{
for(k=0;k<l;k++)
{
mul(x[j+k+l],w[size_x*k/2/l],&product);
add(x[j+k],product,&up);
sub(x[j+k],product,&down);
x[j+k]=up;
x[j+k+l]=down;
}
}
}
}void initw()
{
int i;
w=(complex *)malloc(sizeof(complex)*size_x);
for(i=0;i<size_x;i++)
{
w[i].real=cos(2*PI/size_x*i);
w[i].img=-1*sin(2*PI/size_x*i);
}
}void change()
{
complex temp;
unsigned short i=0,j=0,k=0;
double t;
for(i=0;i<size_x;i++)
{
k=1;j=0;
t=(log(size_x)/log(2));
while((t--)>0)
{j=j<<1;j|=(k&1);k=k>>1;}
if(j>1)
{temp=x[i];x[i]=x[j];x[j]=temp;}
}
}void output()
{
int i;
printf("the result are as follows \n");
for(i=0;i<size_x;i++)
{
printf("%.4f",x[i].real);
if(x[i].img>=0.0001)
printf("+%.4f\n",x[i].img);
else if(fabs(x[i].img)<0.0001)
printf("\n");
else printf("%.4f\n",x[i].img);
}
}void add(complex a,complex b,complex *c)
{
c->real=a.real+b.real;
c->img=a.img+b.img;
}void mul(complex a,complex b,complex *c)
{
c->real=a.real*b.real-a.img*b.img;
c->img=a.real*b.img+a.img*b.real;
}void sub(complex a,complex b,complex *c)
{
c->real=a.real-b.real;
c->img=a.img-b.img;
}
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define N 1000
typedef struct
{
double real;
double img;
} complex;void fft(); //快速傅里叶变换
void initw();
void change();void add(complex,complex,complex *);
void mul(complex,complex,complex *);
void sub(complex,complex,complex *);
void output();complex x(N),*w;
int size_x=0;
double PI;int main()
{
int i,method;
void fft();
void initw();
void change();
void add(complex,complex,complex *);
void mul(complex,complex,complex *);
void sub(complex,complex,complex *);
void divi(complex,complex,complex *); PI=atan(1)*4;
printf("please input the size of x:\n");
scanf("%d",&size_x);
printf("please input the date in x(N):\n");
for(i=0;i<size_x;i++)
scanf("%lf%lf",&x[i].real,&x[i].img);
initw();
output();
return 0;
}void fft()
{
int i=0,j=0,k=0,l=0;
complex up,down,product;
change();
for(i=0;i<log(size_x)/log(2);i++)
{
l=1<<i;
for(j=0;j<size_x;j+=2*l)
{
for(k=0;k<l;k++)
{
mul(x[j+k+l],w[size_x*k/2/l],&product);
add(x[j+k],product,&up);
sub(x[j+k],product,&down);
x[j+k]=up;
x[j+k+l]=down;
}
}
}
}void initw()
{
int i;
w=(complex *)malloc(sizeof(complex)*size_x);
for(i=0;i<size_x;i++)
{
w[i].real=cos(2*PI/size_x*i);
w[i].img=-1*sin(2*PI/size_x*i);
}
}void change()
{
complex temp;
unsigned short i=0,j=0,k=0;
double t;
for(i=0;i<size_x;i++)
{
k=1;j=0;
t=(log(size_x)/log(2));
while((t--)>0)
{j=j<<1;j|=(k&1);k=k>>1;}
if(j>1)
{temp=x[i];x[i]=x[j];x[j]=temp;}
}
}void output()
{
int i;
printf("the result are as follows \n");
for(i=0;i<size_x;i++)
{
printf("%.4f",x[i].real);
if(x[i].img>=0.0001)
printf("+%.4f\n",x[i].img);
else if(fabs(x[i].img)<0.0001)
printf("\n");
else printf("%.4f\n",x[i].img);
}
}void add(complex a,complex b,complex *c)
{
c->real=a.real+b.real;
c->img=a.img+b.img;
}void mul(complex a,complex b,complex *c)
{
c->real=a.real*b.real-a.img*b.img;
c->img=a.real*b.img+a.img*b.real;
}void sub(complex a,complex b,complex *c)
{
c->real=a.real-b.real;
c->img=a.img-b.img;
}
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complex x[N]