CUDA version of word2vec

This CUDA version is carefully checked for correctness.
Achieve about 2.8X faster than CPU-with 8 threads version. (22X faster compare to CPU single thread).





Tools for computing distributed representtion of words
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We provide an implementation of the Continuous Bag-of-Words (CBOW) and the Skip-gram model (SG), as well as several demo scripts.

Given a text corpus, the word2vec tool learns a vector for every word in the vocabulary using the Continuous
Bag-of-Words or the Skip-Gram neural network architectures. The user should to specify the following:
 - desired vector dimensionality
 - the size of the context window for either the Skip-Gram or the Continuous Bag-of-Words model
 - training algorithm: hierarchical softmax and / or negative sampling
 - threshold for downsampling the frequent words 
 - number of threads to use
 - the format of the output word vector file (text or binary)

Usually, the other hyper-parameters such as the learning rate do not need to be tuned for different training sets. 

The script demo-word.sh downloads a small (100MB) text corpus from the web, and trains a small word vector model. After the training
is finished, the user can interactively explore the similarity of the words.

More information about the scripts is provided at https://code.google.com/p/word2vec/