Convenient functions for conversion from and to rata die for a given Gregorian era.

## Usage

``````fixed_from_BP(year, month, day)

fixed_to_BP(object)

fixed_from_BC(year, month, day)

fixed_to_BC(object)

fixed_from_BCE(year, month, day)

fixed_to_BCE(object)

fixed_from_CE(year, month, day)

fixed_to_CE(object)

fixed_from_b2k(year, month, day)

fixed_to_b2k(object)``````

## Arguments

year

A `numeric` vector of years. If `month` and `day` are missing, decimal years are expected.

month

A `numeric` vector of months.

day

A `numeric` vector of days.

object

A `RataDie` object (see `fixed()`).

## Value

• `fixed_from_*()` returns a `RataDie` object.

• `fixed_to_*()` returns a `numeric` vector of Gregorian years.

## Details

The astronomical notation is used for Gregorian years (there is a year 0).

## References

Reingold, E. M. and Dershowitz, N. (2018). Calendrical Calculations: The Ultimate Edition. Cambridge University Press. doi:10.1017/9781107415058 .

Other fixed date tools: `arithmetic`, `as_date()`, `as_decimal()`, `as_fixed()`, `as_year()`, `fixed()`, `fixed_julian`, `format()`, `pretty()`

N. Frerebeau

## Examples

``````## R 1.0.0
(y <- fixed(year = 2000, month = 02, day = 29, calendar = CE()))
#> Rata die: number of days since 01-01-01 (Gregorian).
#> [1] 730179
as_date(y, calendar = CE())
#>   year month day
#> 1 2000     2  29
as_year(y, calendar = CE())
#> [1] 2000.161

## Create a vector of years BP (Gregorian)
## (every two years starting from 2000 BP)
(years <- seq(from = 2000, by = -2, length.out = 10))
#>  [1] 2000 1998 1996 1994 1992 1990 1988 1986 1984 1982
## Convert years to rata die
(rd <- fixed(years, calendar = BP()))
#> Rata die: number of days since 01-01-01 (Gregorian).
#>  [1] -18627 -17897 -17166 -16436 -15705 -14975 -14244 -13514 -12783 -12053
## Convert back to Gregorian years BP
as_year(rd, calendar = BP())
#>  [1] 2000 1998 1996 1994 1992 1990 1988 1986 1984 1982

## More convenient
(rd <- fixed_from_BP(years))
#> Rata die: number of days since 01-01-01 (Gregorian).
#>  [1] -18627 -17897 -17166 -16436 -15705 -14975 -14244 -13514 -12783 -12053
fixed_to_BP(rd)
#>  [1] 2000 1998 1996 1994 1992 1990 1988 1986 1984 1982
``````