Beau Webber schrieb: > > Given a 3 column array A of x,y,z numbers, defining a set of spatial > coordinates, and a binary or logical selection vector S (with as many > elements as rows in A) : > > How do I express the operation of selecting an array R with the set of > those co-ordinates in A where S is 1 (or true) ? > > In Apl I write this as R <- S / A . > > But a referee of a paper is asking that I express this in standard > maths, and I have not yet managed to find an appropriate mathematical > expression. > Cheers for any help, > Beau
I can imagine that referees don't like mathematical explanations in terms of APL - unless yours is a paper about APL (does the language still exist?). But I can't think of an elegant way to express this in standard vector notation either. This newsgroup is only concerned with the development and application of computer-algebra systems like Maxima or Maple, I am therefore widening the audience to include sci.math.