static void init_kernel(int z, int fftlen, kernel * kern)
{
int numkern;
fcomplex *tempkern;
kern->z = z;
kern->fftlen = fftlen;
kern->numbetween = ACCEL_NUMBETWEEN;
kern->kern_half_width = z_resp_halfwidth((double) z, LOWACC);
numkern = 2 * kern->numbetween * kern->kern_half_width;
kern->numgoodbins = kern->fftlen - numkern;
kern->data = gen_cvect(kern->fftlen);
tempkern = gen_z_response(0.0, kern->numbetween, kern->z, numkern);
place_complex_kernel(tempkern, numkern, kern->data, kern->fftlen);
free(tempkern);
COMPLEXFFT(kern->data, kern->fftlen, -1);
}
void rz_interp(fcomplex * data, int numdata, double r, double z,
int kern_half_width, fcomplex * ans)
/* This routine uses the correlation method to do a Fourier */
/* complex interpolation at a single point in the f-fdot plane. */
/* It does the correlations manually. (i.e. no FFTs) */
/* Arguments: */
/* 'data' is a complex array of the data to be interpolated. */
/* 'numdata' is the number of complex points (bins) in data. */
/* 'r' is the Fourier frequency in data that we want to */
/* interpolate. This can (and should) be fractional. */
/* 'z' is the fdot to use (z=f-dot*T^2 (T is integration time)). */
/* 'kern_half_width' is the half-width of the kernel in bins. */
/* 'ans' is the complex answer. */
{
float *dataptr, *respptr;
int ii, numkern, nsum, intfreq, lodata, hidata, loresp, hiresp;
double fracfreq, dintfreq, tmpd, tmpr;
fcomplex *response;
/* Check 'r' and return 0.0 + 0.0i if out of bounds. */
/* Should this return an error and exit instead? */
if (r > numdata - 1.0 || r < 0.0) {
ans->r = 0.0;
ans->i = 0.0;
return;
}
/* Split 'r' into integer and fractional parts */
fracfreq = modf(r, &dintfreq);
intfreq = (int) dintfreq;
/* Return immediately if 'r' is close to an */
/* integer frequency and z is very close to zero */
if (fabs(z) < 1E-4) {
if (fracfreq < 1E-5) {
ans->r = data[intfreq].r;
ans->i = data[intfreq].i;
return;
}
if ((1.0 - fracfreq) < 1E-5) {
ans->r = data[intfreq + 1].r;
ans->i = data[intfreq + 1].i;
return;
}
}
/* Generate the response function */
numkern = 2 * kern_half_width;
response = gen_z_response(fracfreq, 1, z, numkern);
/* Determine the summation boundaries */
lodata = intfreq - kern_half_width;
if (lodata < 0) {
loresp = abs(lodata);
lodata = 0;
} else {
loresp = 0;
}
hidata = intfreq + kern_half_width - 1;
if (hidata > numdata - 1) {
hiresp = numkern - hidata + numdata - 1;
} else {
hiresp = numkern;
}
nsum = hiresp - loresp;
/* Set up our pointers */
dataptr = (float *) (data + lodata);
respptr = (float *) (response + loresp);
/* Do the summation */
ans->r = 0.0;
ans->i = 0.0;
for (ii = 0; ii < nsum; ii++) {
tmpd = *(dataptr++);
tmpr = *(respptr++);
ans->r += tmpd * tmpr + (*dataptr) * (*respptr);
ans->i += (*dataptr) * tmpr - (*respptr) * tmpd;
dataptr++;
respptr++;
}
vect_free(response);
return;
}