mrc-3332 include output in info

[hillalex]

Calls to mod$info() should include details about output as well as internal state variables.

[codecov]

Codecov Report

Merging #105 (e863c45) into master (b0044b2) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #105   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1046      1067   +21     
=========================================
+ Hits          1046      1067   +21     

Impacted Files	Coverage Δ
R/generate_dust.R	100.00% <100.00%> (ø)
R/utils.R	100.00% <100.00%> (ø)

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[richfitz]

I've had a think about the duplication in sorting out indices for output and variables, and have cooked up some suggestions on a PR into this branch (#108). There's still a bit of weirdness (especially around the length calculation) - see what you think.

It took a while to think through because I got quite confused - it turns out that there was an issue in the output indices generated here as the offset was correct only in the case of a single scalar output (see below for an example).

A failing test case

model <- quote({
  initial(x) <- 1
  deriv(x) <- 1
  initial(y[]) <- 1
  deriv(y[]) <- 1
  dim(y) <- 10
  output(a) <- 1
  output(b[]) <- 1
  dim(b) <- 5
})

The expected packing (odin sorts by variables then outputs, and within each sorts by rank).

1  2,    ..., 11,    12, 13,   ..., 17
x, y[1], ..., y[10], a,  b[1], ..., b[5]

You can compare this way, but it's really ugly to do:

gen <- odin::odin(model)
mod <- gen$new()
mod$transform_variables(seq_len(11 + 6))

However, the code in this PR returns incorrect index for output because it's using the total length (17) as the offset to start all output variables at (the len that is passed in).

gen <- odin_dust(model)
mod <- gen$new(list(), 0, 1)
mod$info()$index

Here you can see that we say that a is in 17 and b in 18:22

It's probably worth making a test out of an example like this to prevent regression.

[hillalex]

Thanks, that was a silly bug 🤦 Have added your example as a test