From ripley@stats.ox.ac.uk  Mon Apr  1 21:25:07 2002
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Mon, 1 Apr 2002 22:25:07 +0200 (MET DST)
Subject: [Rd] fft fails for lengths 392, 588, 968, 980 .... (PR#1429)
Message-ID: <200204012025.WAA06636@pubhealth.ku.dk>

R 1.4.1, Linux and Windows

for(i in 1:1000) {
    X <- rnorm(i)
    XX <- fft(fft(X), inverse=T)/i
    if(max(Mod(XX-X)) > 1e-10) print(i)
}

[1] 392
[1] 588
[1] 968
[1] 980

and I then get a segfault during gc().  The answers are way off, with
imaginary parts 1e10 or more.

These numbers are all multiples of 7^2 or 11^2.

(Based on a report to R-help
Date: Thu, 28 Mar 2002 09:37:34 +0100
From: Gabriel Fricout <Gabriel.FRICOUT@cmm.ensmp.fr>
)


-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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[Rd] fft fails for lengths 392, 588, 968, 980 .... (PR#1429)
ripley@stats.ox.ac.uk