The AdjustDateField( d ) command operates on individual fields of the Date object d, adjusting (incrementing or decrementing) the indicated field field by the value amount.

There are two methods by which the indicated date field may be adjusted, "add" or "roll".

The "add" method causes an "overflow" of the indicated field to affect successively larger fields of the date.   For example, adding $50$ days to the day of the month using the "add" method changes the month field, and possibly the year.

The "roll" method applies the indicated adjustment to the indicated date field without affecting other fields of the date. Instead, the amount value is reduced modulo the valid values of field in the case that these are finite in number. For instance, adding $20$ to the day of the week is equivalent to adding $6$ to the day of the week, because $20$ and $6$ are equivalent modulo $7$.

The field names that can be adjusted by AdjustDateField are as follows.

$\mathrm{with}\left(\mathrm{Calendar}\right)\:$

$d≔\mathrm{Date}\left(1995\,9\,23\,4\,2\right)$

$d≔\mathrm{<Date:\; 1995-09-23T04:02:00\; GMT>}$

$\mathrm{AdjustDateField}\left(d\&comma;''day\_of\_week''\&comma;-3\right)$

$\mathrm{<Date:\; 1995-09-20T04:02:00\; GMT>}$

$\mathrm{AdjustDateField}\left(d\&comma;''meridian''\&comma;111\right)$

$\mathrm{<Date:\; 1995-11-17T16:02:00\; GMT>}$

The Calendar[AdjustDateField] command was introduced in Maple 2018.

For more information on Maple 2018 changes, see Updates in Maple 2018.