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# Persian Date leap year calculation¶

There is two popular way to determining leap years for the Persian calendar. astronomical: occur whenever that number of days elapse between equinoxes at the reference meridian.

algorithmic: based on Ahmad Birashk proposed algorithm.

After version 0.3.0 persianDate support both algorithm and you can choose which algorithm use in your project. currently we have support 3 type of calendar `astronomical`, `algorithmic`.

you can change it globally like this example.

# Test leap years calculation algorithm¶

I designed a test to understand the differences between these algorithms.

Check total leap years in next 3003 year after 1396, Difference test between Astronomical, Algorithmic and some other algorithms I found.

you can see this result by run mocha test.

### Check total leap years in next 3003 year, Difference algorithm¶

```- Total gregorian leap year: 728
- Total Nasa algorithm leap year: 727
- Total Algorithmic leap year: 727
- Total Astronomical leap year: 727
- Total Behrooz_Birashk leap year: 727
- Total Wikipedia python code leap year: 727

- Total Common leap year (persianAstro, persianAlgo, NASA, Behrooz_Birashk, wiki python, gregorian): 118

- Common leap year (Astronomical, NASA): 118
- Common leap year (Algorithmic, NASA): 727

- Common leap year (Astronomical, Behrooz_Birashk): 133
- Common leap year (Algorithmic, Behrooz_Birashk): 691

- Common leap year (Astronomical, wiki): 118
- Common leap year (Algorithmic, wiki): 711
```