fix bugs in iubf when faced unintended input

[Koohoko]

Hi Developers,

Recently I have been using iubf for optimising parameters in a spatPomp model. I find some codes in the iubf function did not behave as expected with some particular input. Here I propose changes in a few lines in the R/iubf.R to fix potential bugs.

1. log_cond_densities[neighbor_u, ] on this line will cause "out of bounds" error when Nrep_per_param = 1. So I added a check for this, otherwise we may consider forcing Nrep_per_param to be greater than 1.

2. The def_resample on this line can result in a NULL vector (vector of length 0), if all param_resamp_log_weights are the same. This can happen e.g. for $t_0$, when all observations are at the initial condition and adjusting parameters does have effect on the dmeasure results. A def_resample of length 0 will cause error when sampling it on this line. To fix this, I added a check testing the length of def_resample.

3. Still for the same code chunk as mention in the previous point, there is a special case need to be addressed when length(def_resample) = 1. The sample function will behave differently if the input is an integer of length 1, comparing to when usually we expect the input def_resample is a vector of length > 1. For example when def_resample equals to an index 3, we want resampling $3$, rather than resampling ${1, 2, 3}$, for multiple times. To fix this, I added a special case for length(def_resample) = 1 here.

Please review if this can be helpful. Thank you so much again for this package.

Best,
Haogao

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.

Project coverage is 99.92%. Comparing base (0332b11) to head (bef1b1e).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##            master      #28      +/-   ##
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- Coverage   100.00%   99.92%   -0.08%     
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  Files           54       54              
  Lines         4858     4864       +6     
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+ Hits          4858     4860       +2     
- Misses           0        4       +4     

[ionides]

Hi Haogao, thanks for this collection of improvements. I have merged them and will add unit tests shortly.