/*直接型IIR濾波器*/

#include "math.h"
#include "stdio.h"
#include "stdlib.h"
void filter(b,a,m,n,x,len,px,py)
int m,n,len;
double a[],b[],x[],px[],py[];
{int k,i;
for(k=0;k<len;k++)
{px[0]=x[k];
x[k]=0.0;
for(i=0;i<=m;i++)
{x[k]=x[k]+b[i]*px[i];}
for(i=1;i<=n;i++)
{x[k]=x[k]-a[i]*py[i];}
if(fabs(x[k])>1.0e10)
{printf("This is an unstable filter!\n");
exit(0);
}
for(i=m;i>=1;i--)
{px[i]=px[i-1];}

for(i=n;i>=2;i--)
{py[i]=py[i-1];}
py[1]=x[k];
}
}