Add test for Gradient().
Add test for Gradient().


palashahuja/mlpack,bmswgnp/mlpack,theranger/mlpack,Azizou/mlpack,ajjl/mlpack,ranjan1990/mlpack,palashahuja/mlpack,bmswgnp/mlpack,stereomatchingkiss/mlpack,ersanliqiao/mlpack,ajjl/mlpack,Azizou/mlpack,lezorich/mlpack,thirdwing/mlpack,bmswgnp/mlpack,BookChan/mlpack,ranjan1990/mlpack,darcyliu/mlpack,thirdwing/mlpack,erubboli/mlpack,ranjan1990/mlpack,ersanliqiao/mlpack,BookChan/mlpack,Azizou/mlpack,palashahuja/mlpack,datachand/mlpack,stereomatchingkiss/mlpack,trungda/mlpack,BookChan/mlpack,ersanliqiao/mlpack,darcyliu/mlpack,erubboli/mlpack,datachand/mlpack,chenmoshushi/mlpack,thirdwing/mlpack,trungda/mlpack,minhpqn/mlpack,theranger/mlpack,chenmoshushi/mlpack,minhpqn/mlpack,theranger/mlpack,ajjl/mlpack,lezorich/mlpack,datachand/mlpack,chenmoshushi/mlpack,lezorich/mlpack,minhpqn/mlpack,erubboli/mlpack,darcyliu/mlpack,stereomatchingkiss/mlpack,trungda/mlpack