Module melange::backprop::core_ops

core_ops contains basic mathematical operations at the variable level that rely on the implementation of the tensor module.

Operands are moved, their values are used to compute the value of the resulting variable. Operands are eventually moved in the backpropagation closure if needed.

Since operands are smart poiters (Variable contains a combination of Rc and RefCell) only the "reference" is moved and cloning is costless.