Fall 2018 - I had Arnold for Math 32A and I loved having him as a professor. He comes off as kind of shy and quiet but he's very funny and does a fantastic job of explaining the material. Both midterms were fairly easy and the final had two "curve-setting" questions that were difficult for most people. His homeworks are also really short (3/4 problems per week) but they make you think about the material in a critical way. Overall, I definitely recommend Arnold as a professor, but make sure to put in a lot of effort to do well.