Determining the right relative and absolute tolerances

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bayern science
bayern science am 1 Aug. 2011
Bearbeitet: Torsten am 5 Jan. 2025
My program generates an essentially sinusoidal output. Using the various relative and absolute tolerances I obtained the following fits to a sine function (with about 2e4 data points):
ReTol = 1e-5, AbTol = 1e-7, Sinefit amplitude = 22.1383, phase = -0.10532, fminsearch err = 71211.296;
ReTol = 1e-5, AbTol = 1e-8, Sinefit amplitude = 22.1383, phase = -0.10532, fminsearch err = 71211.296;
ReTol = 1e-6, AbTol = 1e-7, Sinefit amplitude = 24.5425, phase = +0.22298, fminsearch err = 61670.879;
ReTol = 1e-6, AbTol = 1e-8, Sinefit amplitude = 24.5335, phase = +0.22210, fminsearch err = 106022.2668;
I tend to choose ReTol = 1e-5, AbTol = 1e-7, as reducing absolute tolerance doesn't change the result. However if I reduce relative tolerance I obtain different results (especially the phase). Thus what should I choose? ReTol = 1e-5, AbTol = 1e-7, or ReTol = 1e-6, AbTol = 1e-7?
  11 Kommentare
sajjad
sajjad am 5 Jan. 2025
I am not receiving more output yet.
Torsten
Torsten am 5 Jan. 2025
Bearbeitet: Torsten am 5 Jan. 2025
As I answered in another question of yours
, it's impossible to get more maxima because the number of maxima if given by the solution of the PDE system. E.g. if your solution were y(x)=sin(x), you would get maxima and minima at odd multiples of pi/2, and no modification of the code could give you more of them. Or do I get wrong what you are asking for ?

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