The data model can be NULL
for none.
Otherwise M
is a vector of function names and arguments.
Example:
M = c("log","season",12,"trend",1)
The above model
takes the log of the data, then subtracts a seasonal component
of period 12, then subtracts a linear trend component.
These are the available functions:
diff | Difference the data. Has a single argument, the lag. |
hr | Subtract harmonic components. Has one or more
arguments, each specifying the number of observations per harmonic. |
log | Take the log of the data, has no arguments. |
season | Subtract a seasonal component.
Has a single argument, the number of observations per season. |
trend | Subtract a trend component.
Has a single argument, the order of the trend
(1 linear, 2 quadratic, etc.) |
At the end of the model there is an implicit subtraction of the mean operation.
Hence the resulting time series always has zero mean.