Debugging odin models can be challenging because:
Here, we outline some strategies for debugging, and describe the new features that aim to make this easier.
print()
As of odin 1.4.5, you can print the value of some variables in the middle of running your model. We will expand and change this functionality in future versions, your feedback is very welcome.
Consider the simple model below, which illustrates the idea:
## Loading required namespace: pkgbuild
## Generating model in c
## ℹ Re-compiling odin156e6554 (debug build)
## ── R CMD INSTALL ───────────────────────────────────────────────────────────────
## * installing *source* package ‘odin156e6554’ ...
## ** using staged installation
## ** libs
## using C compiler: ‘gcc (Ubuntu 13.2.0-23ubuntu4) 13.2.0’
## gcc -I"/usr/share/R/include" -DNDEBUG -fpic -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -ffile-prefix-map=/build/r-base-4sITk6/r-base-4.4.2=. -fstack-protector-strong -fstack-clash-protection -Wformat -fcf-protection -fdebug-prefix-map=/build/r-base-4sITk6/r-base-4.4.2=/usr/src/r-base-4.4.2-1.2404.0 -Wdate-time -D_FORTIFY_SOURCE=3 -UNDEBUG -Wall -pedantic -g -O0 -c odin.c -o odin.o
## odin.c: In function ‘odin_metadata’:
## odin.c:76:18: warning: unused variable ‘internal’ [-Wunused-variable]
## 76 | odin_internal *internal = odin_get_internal(internal_p, 1);
## | ^~~~~~~~
## gcc -I"/usr/share/R/include" -DNDEBUG -fpic -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -ffile-prefix-map=/build/r-base-4sITk6/r-base-4.4.2=. -fstack-protector-strong -fstack-clash-protection -Wformat -fcf-protection -fdebug-prefix-map=/build/r-base-4sITk6/r-base-4.4.2=/usr/src/r-base-4.4.2-1.2404.0 -Wdate-time -D_FORTIFY_SOURCE=3 -UNDEBUG -Wall -pedantic -g -O0 -c registration.c -o registration.o
## gcc -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -flto=auto -ffat-lto-objects -Wl,-z,relro -o odin156e6554.so odin.o registration.o -L/usr/lib/R/lib -lR
## installing to /tmp/RtmpJSotBe/devtools_install_a0f681206b6/00LOCK-filea0f2f5a7fb7/00new/odin156e6554/libs
## ** checking absolute paths in shared objects and dynamic libraries
## * DONE (odin156e6554)
## ℹ Loading odin156e6554
## [0.000000] x: 1.000000
## [0.000100] x: 1.000100
## [0.000100] x: 1.000100
## [0.000200] x: 1.000200
## [0.000200] x: 1.000200
## [0.020796] x: 1.021012
## [0.020796] x: 1.021014
## [0.041392] x: 1.042257
## [0.041392] x: 1.042262
## [0.061987] x: 1.063947
## [0.061987] x: 1.063951
## [0.121251] x: 1.128890
## [0.121251] x: 1.128907
## t x
## 1 0.0 1.000000
## 2 0.1 1.105171
Here we’ve told odin that we want to watch the variable
x
and print its value at every evaluation (the third line
of the model code) and to include generated code that actually prints
the debugging information (debug_enable = TRUE
). When we
run the model it prints out the time in square brackets then the debug
information following. Notice that we only requested the solution at
times 0 and 0.1 but the debug information shows every point in time that
the ODE solver evaluated this system of equations.
While this function shares its name with R’s print()
it
has entirely different functionality.
Importantly, adding the print()
statement to a model has
no effect unless it is compiled with debug_enable = TRUE
.
It’s safe to leave these statements in with no performance cost as if
debug_enable = FALSE
(the default) odin will simply not
generate any related code.
print
format stringsFor print formatting, we use glue to drive the formatting, and if you have used that package the format will feel familiar.
The most simple usage is as above; you can refer to variables within
{curly braces}
; so long as your variable is a scalar this
will work. Outside of curly braces the string is printed verbatim.
If your model takes many steps, or if you want to narrow down on a
problem, you may want to enable conditional display of your debug
information. Use the argument when =
to control display,
such as
which will display the value of x
when it is greater
than 1. You can chain together expressions with parentheses and
&&
or ||
and reference any value in
your system. For example:
You can control the way that quantities are displayed through the use of formatting options. The formatting is the same as used by R, so you can experiment in the console easily. The default is to print as a generic floating point number, so this:
is roughly equivalent to writing
See ?sprintf
for more information; but this defaults to
6 decimal places of precision. This may not be appropriate if you are
dealing with numbers that are very large or very small; these both look
a bit silly:
## [1] "x: 0.000000, y: 10000000.000000"
The first loses all information - the only non-zero parts of the number fall after the precision cut-off, while in the second the 6 decimal places just add noise. So above we might prefer:
## [1] "x: 1e-07, y: 1e+07"
which we could write in odin’s approach as
Anything after the ;
is interpreted as a format
specifier. You could also do
which would format y
to 2 decimal places. We follow here
the example of the sprintf
transformer example in glue by not including the %
placeholder, but allow all formats that the underlying library
supports.
This is an experimental interface, and it has not been exposed to much real-world use. As such it is possible that you might write fairly innocent looking code and it produce a compiler error rather than a nicer R error - please let us know so we can fix this.
print
{x; d}
) for
variables that are merely integer-like, or you will get unexpected junk
output out.