[mlpack-git] [mlpack] add a wrapper for the matrix completion SDP (#374)

[Ryan Curtin]

> +
> +MatrixCompletion::MatrixCompletion(const size_t m,
> +                                   const size_t n,
> +                                   const arma::umat& indices,
> +                                   const arma::vec& values)
> +  : m(m), n(n), indices(indices), values(values),
> +    sdp(indices.n_cols, 0, CreateInitialPoint(m, n, DefaultRank(m, n, indices.n_cols)))
> +{
> +  checkValues();
> +  initSdp();
> +}
> +
> +void MatrixCompletion::checkValues()
> +{
> +  if (indices.n_rows != 2)
> +    Log::Fatal << "indices.n_rows != 2" << std::endl;

Can you make these error messages more descriptive?  Should a user come up against this (say they are using CF or something), they're just going to see

```
[FATAL] indices.n_rows != 2
```

and confusion will reign forever.  Probably `MatrixCompletion::MatrixCompletion(): matrix of indices for constraints does not have two rows.` or something similar will be better.  Alternately, I am beginning to think that `Log::Fatal` calls should produce a backtrace, but I want to let the idea simmer more before opening an issue or doing something about it (getting backtraces is not always easy, and I don't think the code we have in place for `Log::Assert` is very robust).

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Reply to this email directly or view it on GitHub:
https://github.com/mlpack/mlpack/pull/374/files#r22744211
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