41 lines
999 B
C
41 lines
999 B
C
#include "bessels.h"
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#include <stdlib.h>
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#include <math.h>
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static const double ln2 = 0.69314718055994531;
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#include <stdio.h>
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// general; gives an array of size
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complex double * hankelcoefftable_init(size_t maxn) {
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complex double *hct = malloc((maxn+1)*(maxn+2)/2 * sizeof(complex double));
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for(size_t n = 0; n <= maxn; ++n) {
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complex double *hcs = hankelcoeffs_get(hct,n);
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for (size_t k = 0; k <= n; ++k) {
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double lcoeff = lgamma(n+k+1) - lgamma(n-k+1) - lgamma(k+1) - k*ln2;
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printf("%f, %.16f\n", lcoeff, exp(lcoeff));
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// for some reason, casting k-n to double does not work,so
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// cpow (I, k-n-1) cannot be used...
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complex double ifactor;
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switch ((n+1-k) % 4) {
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case 0:
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ifactor = 1;
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break;
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case 1:
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ifactor = -I;
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break;
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case 2:
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ifactor = -1;
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break;
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case 3:
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ifactor = I;
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break;
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}
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// the result should be integer, so round to remove inaccuracies
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hcs[k] = round(exp(lcoeff)) * ifactor;
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}
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}
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return hct;
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}
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