Debugging the R model

In theory, the TMB and R output of gadget3 should be identically-behaving functions, so instead of trying to decipher what the TMB model is doing wrong, you can use R function instead in a more familiar environment, for example using standard tools such as options(error=recover).

You can also use edit() to edit the R function directly and re-run the model:

# Model setup will look something like this
ling_model <- g3_to_r(...)

ling_model <- edit(ling_model) ; ling_model(ling_param)

…this is useful if you want to add trace print() statements around a particular part of the model that’s failing, e.g. or insert a breakpoint by adding a recover() line.

Debugging the TMB model

It’s possible to have a working R model that doesn’t compile using TMB, due to the relative strictness of the Eigen array library in comparison to R arrays, for example. In which case you’ll need to debug the TMB version.

Preserving your R session whilst building

If the model crashes whilst forming the TMB ADFun object, then it takes your R session with it. To prevent this, wrap g3_tmb_adfun() with TMB::gdbsource() as follows:

# Model setup will look something like this
tmb_ling <- g3_to_tmb(...)
tmb_param <- attr(tmb_ling, 'parameter_template')

writeLines(TMB::gdbsource(g3_tmb_adfun(
    tmb_ling,
    tmb_param,
    compile_flags = "-g",
    output_script = TRUE)))

output_script = TRUE tells g3_tmb_adfun() to, after compilation, write a temporary R script that will build the TMB ADFun object (and presumably crash in the process). TMB::gdbsource() in turn runs a provided R script in a fresh R session wrapped in gdb. By default it will print a stacktrace and quit, which should show you where the crash occured.

Editing C++ code

As with the R model you can edit the raw C++ source before building:

tmb_ling <- edit(tmb_ling)
writeLines(TMB::gdbsource(g3_tmb_adfun(
    tmb_ling,
    tmb_param,
    compile_flags = "-g",
    output_script = TRUE)))

Through this you can…

  • Print the contents of single values with std::cout << ling__Linf << std::endl;
  • Use ().cols() and ().rows() to get the size of an array expression
  • Print the contents of array objects with ling_imm__consratio.print()

Interactive debugging

In theory you can use interactive = TRUE with TMB::gdbsource(), however as this eats error messages it’s better to do this by hand:

> g3_tmb_adfun(tmb_ling, tmb_param, compile_flags = "-g", output_script = TRUE)
[1] "/tmp/RtmpysTVvW/file3da4a6f13a80c.R"

R -d gdb
(gdb) run --vanilla < /tmp/RtmpysTVvW/file3da4a6f13a80c.R
 . . . Compilation, crash at some point . . .
(gdb) up
(gdb) up
(gdb) up
(gdb) call ling_imm__consratio.print()
Array dim: 35 1 8
Array val: -nan -nan -nan -nan
(gdb) call ling_imm__num.print()
Array dim: 35 1 8
Array val: -nan -nan -nan -nan -nan

(gdb) print cur_time
$5 = 0

Note that for the .print() method to be available for arrays, it has to be referenced at least once in the model source, otherwise it won’t be compiled in. Use edit(tmb_ling) to add it somewhere first.