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

GRAHĀNAYANĀDHYĀYA ग्रहानयनाध्यायः
Verse 1. To Compute the Ahargaṇa the collection of
days from the beginning of Kalpa ie from the beginning
of creation. Multiply the number of sidereal solar years
from the beginning of Kalpa by 12; add the number of
elapsed lunar months ; multiply by thirty ; add the number
of elapsed tithis. Let this number be x. Then [ (x × A) / s ]
the integral number obtained by dividing the product of x
and A the number of Adhikamāsas in a Kalpa by s the
number of solar days thereof gives the number of elapsed
Adhikamāsas. Multiply this number of Adhikamāsas by
30 and add to x. The result gives the number of elapsed
tithis, Let this be y. Then [ (y × K) / T ] the integral num-
ber obtained by dividing the product of y and K the num-
ber of Kshayāhas in a Kalpa by T the number of Tithis in
a Kalpa, gives the number of Kshayāhas. Subtracting this
number from y, we have the Ahargaṇa ie the number of the
elapsed civil days from the beginning of Kalpa. This
Ahargaṇa has its beginning on Sunday and is itself consti-
tuted of mean solar days. While computing the Adhika-
māsas or Kshayāhas, the integral numbers of the quosients
alone should be taken rejecting the remainders.
Comm. The elapsed number of solar years is directed
to be multiplied by 12 in the beginning. This number
does not constitute purely solar years. Solarity was
secured upto the point of the last intercalation of an Adhi-
kamāsa and thereafter one or two luni -solar years would
have been added. But Construing these one or two luni-
solar years as mean solar years does not make a difference
while computing the Adhikamāsas, for the following reason.
Adhikamāsas normally occur once in three years. Even