Function eval

Core/Variational/utils.cpp:7–13

namespace Variational {

MatrixXd eval(var root, bool iter){
    expression exp(root);
    if(iter)
        return exp.propagate(exp.findLeaves());
    else
        return exp.propagate();
}

void back(const var& root, 
        std::unordered_map<var, MatrixXd>& derivative){