[write and read functions for AdaGrad](https://github.com/IllinoisCogComp/lbjava/blob/master/lbjava/src/main/java/edu/illinois/cs/cogcomp/lbjava/learn/AdaGrad.java#L334-L336) are not written Examples are here: https://github.com/IllinoisCogComp/lbjava/blob/master/lbjava/src/main/java/edu/illinois/cs/cogcomp/lbjava/learn/StochasticGradientDescent.java#L260-L294
