Abbas Edalat

I was very sorry to read that Abbas Edalat, a professor of Computer Science at Imperial College, had been arrested while attending an academic function in Iran. I don’t know the man but I do know and admire some of his work. It may seem a bit tasteless to talk about that and not his appalling predicament, but of that I am totally ignorant. Most readers will be aware that the standard formats for representing numbers in a computer are the IEEE formats, and that the laws of algebra only hold approximately for them. The point of the IEEE floating point formats is that all numbers use a fixed number of bytes for their representation. There are, however, other formats for real numbers, for which the rules of algebra hold to within any specified precision, but they come with a penalty, in terms of memory consumed and time of calculation. Edalat’s doctoral thesis was on this topic.