Example error message
You have requested a date Sequence with dateUnit: "M" (month) with a non-integer step. Since the size of a non-integer step varies with month, this is ambiguous. The resulting dates in the Sequence will fall on even month increments.
This results from using a non-integer step size with the Sequence function along with a «dateUnit» of "WD", "M" or "Y", as in this example:
Sequence(1-Jan-2011, 31-Dec-2020, 0.4, dateUnit: "M")
The problem here is that 0.4 months is not a consistent number. Depending on the number of days in the month, that might be 11 days, 4 hours and 48 minutes, 11 days 14 hours and 24 minutes, 12 days exactly or 12 days 9 hours and 36 minutes. So how big of a step size is being requested here? Instead of picking one of these arbitrarily, Analytica issues this warning and then produces a sequence where each step is an even integer month from the previous date, but where over the course of a long sequence the average step is 0.4. In this example the following series would result:
[1-Jan-2011, 1-Jan-2011, 1-Feb-2011, 1-Feb-2011, 1-Mar-2011, 1-Mar-2011, 1-Mar-2011, 1-Apr-2011, 1-Apr-2011, 1-May-2011, ... ]
When you want a fractional increment, it is preferable to specify a smaller date unit. For example, if you want a 15-day increment, use:
Sequence(1-Jan-2011, 31-Dec-2010, 15, dateUnit: "D")