Useful computations need useful numbers

Abstract

Most of us have taken the exact rational and approximate numbers in our computer algebra systems for granted for a long time, not thinking to ask if they could be significantly better. With exact rational arithmetic and adjustable-precision floating-point arithmetic to precision limited only by the total computer memory or our patience, what more could we want for such numbers? It turns out that there is much more that can be done that permits us to obtain exact results more often, more intelligible results, approximate results guaranteed to have requested error bounds, and recovery of exact results from approximate ones.