This issue came to my attention from Math.SE: https://math.stackexchange.com/questions/1015325/is-the-derivative-of-x-on-0-1-always-equal-to-1/1015342#1015342
To summarize, it appears that Mathematica gives erroneous results when computing the numerical value of the derivative of FractionalPart
: the command
Plot[FractionalPart'[x], {x, 0, 2}, WorkingPrecision -> 100,
MaxRecursion -> 8, PlotPoints -> 100, PlotRange -> {-2, 4}]
generates the following graph:
Verification and/or explanation for this phenomenon is most welcome.