Dear R-Users, I suspected it is a catastrophic loss of precision. Unfortunately, it popped up in an unexpected way. I was plotting some curves using the Bessel function , something like this:
curve(besselJ(x, pi/2-x), 0, 2*pi, ylim = c(-2,2), n = 101) abline(v = pi/2, col = "red", lty = 2) # n = 101 is the default; Note that the error is generated for a large set of values of x: median (besselJ(seq(0, 1, length.out = 1025), 1E-15)) # 9.38233e+14 Sincerely, Leonard ________________________________ From: Leo Mada <[email protected]> Sent: Sunday, December 28, 2025 6:28 PM To: Leo Mada via R-help <[email protected]> Subject: Error in besselJ(pi/2, 1E-15)? Dear R-Users, besselJ(pi/2, 0) # 0.4720012 besselJ(pi/2, 1E-14) # 0.4720012 besselJ(pi/2, 1E-15) # 4.720012e+14 There seems to be an error in besselJ(pi/2, eps), where eps is close to 0; although besselJ(pi/2, 0) is well behaved. I am not an expert in the field - but it doesn't seem right. Sincerely, Leonard [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
