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 Routine not functioning properly
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kepler
Junior WebHelper
Junior WebHelper


Joined: 08 Feb 2002
Posts: 37

PostPosted: Mon Oct 11, 2004 1:43 pm (13 years ago) Reply with QuoteBack to Top

Hi,

I have a routine with the following structure:

void GetGST(double jed, int s, double gst) {
(...code goes here to determine gst)
}

The problem is that, in a loop statement, I call the routine for the first time and it returns a valid value; in the following calls it gives results without sense! For instance, it gives first 6.5 ( it nevers supose to give values greater that two PI ), and in the second call it gives 1000!

I used also the code:

void GetGST(double jed, int s, double *gst) {
(...code goes here to determine *gst)
}

but the same thing happens.

What am I doing wrong?

Best regards,

Kepler
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adam
Forum Moderator & Developer



Joined: 26 Jul 2002
Posts: 704
Location: UK

PostPosted: Mon Oct 11, 2004 2:28 pm (13 years ago) Reply with QuoteBack to Top

Without the actual code it's going to be impossible to debug this, is it possible for you to give us some more code?

________________________________
It's turtles all the way down...
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kepler
Junior WebHelper
Junior WebHelper


Joined: 08 Feb 2002
Posts: 37

PostPosted: Wed Oct 13, 2004 7:25 am (13 years ago) Reply with QuoteBack to Top

Here it is:

void GetGST(double jed, int s, double gst) {

static double jedz, sz;
double T, dpsi, deps, dpsidot, depsdot;
double meaneps, trueeps, meanepsdot, trueepsdot, eqeqnx, eqeqnxdot;

if ((jed == jedz) && (s == sz)) return;
jedz = jed;
sz = s;

T = (jed - J2000) / JulCty;

/* compute GMST in seconds */
gst = 67310.54841 + T * ((876600.0 * 3600.0 + 8640184.812866)
+ T * (0.093104 + T * (-0.0000062)));

/* convert to radians */
gst = amodulo(gst / 3600.0, 24.0) * H2R;

if (s == 1) {
/* get nutation quantities */
GetDpsiDeps(jed, &dpsi, &deps, &dpsidot, &depsdot);

/* get mean obliquity */
Obliquity(J2000, jed, 0, &meaneps, &meanepsdot);

/* get true obliquity */
Obliquity (J2000, jed, 1, &trueeps, &trueepsdot);

/* get equation of the equinoxes */
eqeqnx = dpsi * cos(trueeps);
eqeqnxdot = dpsidot * cos(trueeps) - dpsi * trueepsdot * sin(trueeps);
gst += eqeqnx;
}

gst = amodulo(gst, TWOPI);
}

It works at the first call only.

Regards,

Kepler
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