I was lucky to have the office across the hall from him at MathWorks around 2000. He was always interested in chatting with whomever came by and learning about what they were working on. He was always a college professor at heart.

He called me into his office one day to play me a voicemail. It was Steve Jobs asking him what he could do to get MATLAB shipping on the Mac again.

MathWorks had dropped the platform because of it's then-low market share. Steve was having trouble selling Macs to universities because MATLAB was so important there. Apple ended up sending MathWorks a bunch of Macs for the build-end-test system, and MATLAB did soon return to the Mac.

Penny Anderson was in his office one day. They were trying to figure out which LAPACK numerical algorithm to use under the covers to power some MATLAB function. The different algorithms performed better for different types of matrices and different hardware specifications. They were trying to work out some heuristic where they could automatically pick the right one for the user, but they were having trouble coming up with reliable rules. Finally, Penny proposed exposing it as an option so the user could specify the one they wanted. Cleve responded with something like "If you and I can't figure out which algorithm to use, our customers have no chance. So let's just pick the one that usually works well and not make them try guess."