See "A Direct Adaptive Method for Faster Backpropagation Learning: The RPROP Algorithm",
M. Riedmiller and H. Braun,
Proceedings of the 1993 IEEE International Conference on Neural Networks,
pp. 586-591
This is the orginal version of the algorithm. There are many later variations.

(c) Dr. James McCaffrey
https://visualstudiomagazine.com/articles/2015/03/01/resilient-back-propagation.aspx
https://jamesmccaffrey.wordpress.com/2015/03/20/neural-network-resilient-back-propagation-rprop-using-c/