[Kstars-devel] question about KSUtils::lagrangeInterpolation()

[Jason Harris]

Hello,

The lagrangeInterpolation() function is used to determine the exact 
moment at which an equinox or solstice occurs, by interpolating from 5 
measurements of the Sun's ecliptic longitude (as determined at noon on 
each of 5 days surrounding the target event).

However, as the function is written, the interpolated Julian Day number 
is returned as a double, which is then recast as a 'long double'.

Since doubles have 10-digit precision, this means the solstice/equinox 
times will only be accurate to +/1.5 minutes.  I suggest we change 
lagrangeInterpolation() so that it uses long doubles internally.  

Alternatively, we could subtract the JD of one of the measured points 
from each of them, so that ten digits would be sufficient precision.

What do you think?

regards,
Jason 
-- 
KStars: A KDE Planetarium
http://edu.kde.org/kstars