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/* determine small t */
#ifndef lint
static const char SCCSID[]="@(#)pj_tsfn.c 4.3 93/06/12 GIE REL";
#endif
#include <math.h>
#define HALFPI 1.5707963267948966
double
pj_tsfn(double phi, double sinphi, double e) {
sinphi *= e;
return (tan (.5 * (HALFPI - phi)) /
pow((1. - sinphi) / (1. + sinphi), .5 * e));
}
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