R devel - Jan 2025 - Possible issue in stats/arima.R package

Hello all,

I am running R version 4.4.2 (2024-10-31 ucrt) on Windows 10 x64, and
noticed something that might be a minor bug (or at least inconsistent code)
in the stats/arima.R package.
I have found:
1. A missing stop() call at line 69:
    if (length(order) == 3) seasonal <- list(order = seasonal) else
("\'seasonal\' is of the wrong length")
it should be rather:
    if (length(order) == 3) seasonal <- list(order = seasonal) else
stop("\'seasonal\' is of the wrong length")

2. An unused 'mod' variable assignment at line 190:

mod <- makeARIMA(trarma[[1]], trarma[[2]], Delta, kappa, SSinit)

I am trying to confirm whether this is intended behavior or possibly an
overlooked detail. Could someone please clarify if the current logic is
correct?

Thank you.

Best regards,
Norbert Kuder

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On 2025-01-02 9:04 a.m., Norbert Kuder wrote:
> Hello all,
> 
> I am running R version 4.4.2 (2024-10-31 ucrt) on Windows 10 x64, and
> noticed something that might be a minor bug (or at least inconsistent code)
> in the stats/arima.R package.
> I have found:
> 1. A missing stop() call at line 69:
>      if (length(order) == 3) seasonal <- list(order = seasonal) else
> ("\'seasonal\' is of the wrong length")
> it should be rather:
>      if (length(order) == 3) seasonal <- list(order = seasonal) else
> stop("\'seasonal\' is of the wrong length")
I think you're right about this one.
> 
> 2. An unused 'mod' variable assignment at line 190:
> 
> mod <- makeARIMA(trarma[[1]], trarma[[2]], Delta, kappa, SSinit)
> 
> I am trying to confirm whether this is intended behavior or possibly an
> overlooked detail. Could someone please clarify if the current logic is
> correct?
> 
In the R-devel source I see mod being used in the next statement:

         mod <- makeARIMA(trarma[[1L]], trarma[[2L]], Delta, kappa, SSinit)
         val <- if(ncxreg > 0L)
             arimaSS(x - xreg %*% coef[narma + (1L:ncxreg)], mod)
         else arimaSS(x, mod)

It appears in both alternatives of the if statement.

This one is strange though:  the code in the github mirror 
(https://github.com/wch/r-source/blob/4a1ed749271c52e60a85e794e6f34b0831efb1ae/src/library/stats/R/arima.R#L256-L258)
is different:

         mod <- makeARIMA(trarma[[1L]], trarma[[2L]], Delta, kappa, SSinit)
         if(ncxreg > 0) x <- x - xreg %*% coef[narma + (1L:ncxreg)]
         arimaSS(x, mod)

yet the log shows no recent changes.  I'm not sure what's going on.

Duncan Murdoch