'Returns a keep mask for dropout.
Arguments:
keep (int, optional): the keep threshold. Values smaller than keep
will be set to 0, otherwise set to 1.
out (Tensor, optional): where the result will be stored. If out is
None, only the op-tree will be returned.
Returns:
OpTreeNode: the resulting op-tree'

def dropout(self, keep=0.5, out=None):

    return self.less_equal(self.rand(), keep, out=out)
