# Single Precision a x plus y (SAXPY) terminology

I've been reading books which refers to vector update operations of the form: y := y + ax, where y and x are vector variables and a is a scalar as SAXPY. I understand ax plus y part, but why "single precision"?

I'm seeing it in the context of complexity estimates of iterative linear solvers, where I assume that most variables (the vectors and matrices) are double precision, not single. But vector updates are still described as SAXPY.

Thanks.

• Wow, really? To me, SAXPY really just means 32-bit float or REAL*4 arithmetic, and DAXPY means 64-bit double or REAL*8. In fact, I hear people use the term DAXPY far more often than SAXPY these days, and that makes sense because nobody still uses single precision. – Wolfgang Bangerth Apr 11 '16 at 2:35