Thanks again, @kphng . Another question, since the goal is to minimize error, if there is reward -1, then loss become smaller than a case where there is +1 reward in the (-log_prob * reward). Example:
a) reward -1, prob =0.9 (-log(0.9)*reward), loss = -0.105
b) reward 1, prob =0.9  (-log(0.9)*reward), loss = 0.105
In this scenario, case b has higher error than case a. Am I missing sth here?