Zcosft1.cin: Difference between revisions
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// [[zcosft1.cin]] is C++ routine required for compilation of examples with [[DCTI]], Discrete Fourier transform of the First kind. | // [[zcosft1.cin]] is C++ routine required for compilation of examples with [[DCTI]], Discrete Fourier transform of the First kind. | ||
Latest revision as of 20:52, 9 September 2020
// zcosft1.cin is C++ routine required for compilation of examples with DCTI, Discrete Fourier transform of the First kind.
void zcosft1(z_type y[], int n)
{ /* void zrealft(z_type data[], unsigned long n, int isign);*/
int j,n2; z_type sum,y1,y2;
double theta,wi=0.0,wpi,wpr,wr=1.0,wtemp;
theta=M_PI/n;
wtemp=sin(0.5*theta);
wpr = -2.0*wtemp*wtemp;
wpi=sin(theta);
sum=0.5*(y[1]-y[n+1]);
y[1]=0.5*(y[1]+y[n+1]);
n2=n+2;
for (j=2;j<=(n>>1);j++) {
wr=(wtemp=wr)*wpr-wi*wpi+wr;
wi=wi*wpr+wtemp*wpi+wi;
y1=0.5*(y[j]+y[n2-j]);
y2=(y[j]-y[n2-j]);
y[j]=y1-wi*y2;
y[n2-j]=y1+wi*y2;
sum += wr*y2;
}
zrealft(y,n,1);
y[n+1]=y[2];
y[2]=sum;
for(j=4;j<=n;j+=2) {sum += y[j]; y[j]=sum;}
}