irregular summations in Home/CAS

[Wes Loewer]

I first saw this idea that Σ(..., a, b) = -Σ(..., b+1, a-1) some 20 years ago on the TI-89. It was documented in the TI-89 manual, but it gave no indication as to why. There was an old manual on the shelf at school for its predecessor, Derive (for DOS), which also documented the behavior without explanation.

I had always figured it was the result of some some weird programming artifact. As a result of this thread, I now feel "enlightened" by the mathematical logic.

Thank you and merci beaucoup