First of all, let me say that a few days after I started using "Numerical Recipes in C++", the book migrated from my shelf of software documentation to my shelf of classics. It has what one looks for in a gem- depth and clarity.

I do, however, have a very basic question: What sign should be in the exponent in the definition of the Fourier transform? Part of the reason I ask is that I'm writing a time domain simulator, and I found it a little alarming to see time going backward (!). Since I ran into exactly the same issue in a similar program using the PERL Data Language (PDL), I'm not sure this is an entirely trivial question.

Those showing/implying a "+" sign in the exponent:

"Numerical Recipes in C++", Second edition, pg. 501, eq. 12.0.1

PERL Data Language (PDL) FFT module

Those books on my shelves (some classic, some not, all pretty good) showing a "-" sign in the exponent:

Papoulis, "Probability, Random Variables and Stochastic Processes", McGraw-Hill, 1965, pg. 440, eq. 12-18

Wayland, "Differential Equations Applied in Science and Engineering", Van Nostrand, 1957, pg. 237, eq. 6.88

Gold and Rader, "Digital Processing of Signals", McGraw-Hill, 1969, pg. 159, eq. 6.1

Ramo, Whinnery and Van Duzer, "Fields and Waves in Communications Electronics", Third Edition, Wiley, 1994, pg. 359, eq. 16

Any thoughts/suggestions?

Thanks.
Steinberger