सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

542
zero ?" The answer is t (a + b) / Adya - Anya which gives the time
after which Vaidhṛti is likely to occur.
Suppose a and b the declinations observed at a particular
moment, are one north and and the other south. Compute
their difference a - b; after a few ghatis or days again from
the difference of the declinations c and d ie. c - d. If
c - d < a - b then Vaidhṛti is going to occur, otherwise it
has elapsed. This is so because the difference has to vanish
for Vaidhṛti to occur.
Viewing the situation algebraically, ie. construing
northern declination to be positive and southern negative,
we could have laid down only one criterion, instead of
separating the issues and stipulating separate criteria.
Proceeding on this basis, suppose the the Sun and the Moon
are one in the first quadrant and the other in the second.
Here both declinations are therefore positive. Compute
their difference a - b; compute again the difference of
c and d which are again northern declinations observed
after a few ghatis or days. If c - d < a - b then Vyatīpāta
is going to occur.
Now take a case when one of a and b is north and the
other south ; so also c and d. We are talking of a, c to be
in the first quadrant and b, d in the fourth quadrant. Even
now if c - d < a - b Vyatīpāta is going to occur. Thus
there is no need to stipulate "Sum or difference". Difference
alone counts now, because difference of one positive and the
other negative quantities means sum only. Thus in the
case of Vyatīpāta difference should tend to zero, whether
both the declinations are north, or one north and the other
south.
Similarly in the case of Vaidhṛti the sum should tend
to zero because the algebraic sum of one positive northern
declination and the other negative southern declination