linfa-clustering won't compile due to type error

[quietlychris]

I came across an issue compiling linfa-clustering as a dependency for the Rust-ML book today, which per the error message is tracked down to a link the linfa-clustering/src/gaussian_mixture/algorithm.rs in the compute_precisions_cholesky_full() function, which using the Cholesky method imported in from ndarray-linalg. As far as I can tell, when cloning linfa's master and trying to build in the sub-crate, I run into the same compilation error. I've tinkered around with it, but haven't figured out a fix quite yet.

Compiling linfa-clustering v0.3.1 (https://github.com/rust-ml/linfa?branch=master#b7c31c58)
error[E0599]: no method named `cholesky` found for struct `ArrayBase<ViewRepr<&<F as linfa::Float>::Lapack>, Dim<[usize; 2]>>` in the current scope
   --> /home/chrism/.cargo/git/checkouts/linfa-f557574ebcb8312b/b7c31c5/algorithms/linfa-clustering/src/gaussian_mixture/algorithm.rs:262:51
    |
262 |             let decomp = covariance.with_lapack().cholesky(UPLO::Lower)?;
    |                                                   ^^^^^^^^ method not found in `ArrayBase<ViewRepr<&<F as linfa::Float>::Lapack>, Dim<[usize; 2]>>`

error: aborting due to previous error

[bytesnake]

This was introduced in #121 and happens when you do not specify a LAPACK backend for compilation. I pushed a fix in 6866450

[quietlychris]

Sounds great, thanks!