FIX: Ensure expected behaviour when copy=True|False in Imputer
FIX: Don't copy X at imputation in the sparse case
COSMIT: remove useless import
Update docstring + Use np.diff
Update dpgmm.py

The document has been moved.
Update dp-derivation.rst

The subscript has been mislabeled.
The code use this correct formulae, and can be seen in the thesis --Variational Inference for Dirichlet Process Mixtures David Blei, Michael Jordan. Bayesian Analysis, 2006 as well.
DOC add missing comment for C parameter
DOC remove duplicate reference to example
Merge pull request #2702 from glouppe/imputer-copy

[MRG] Fix #2697 - Copy parameter in Imputer
Merge pull request #2708 from likang7/patch-3

Update dp-derivation.rst
Merge pull request #2706 from likang7/patch-2

Update dpgmm.py
FIX: don't force finite in imputation
FIX: use _assert_all_finite
Merge pull request #2712 from glouppe/imputer-copy

FIX: don't force finite in imputation