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Could it be that plots in log scale use a sampling done in the non-log scale?

There was a problem I thought looked similar: the x-range and y-range for a plot are chosen slightly wider than the actual range of x-values and y-values that occur in the plot, and sometimes in log scale it looks like this "slightly wider" is chosen in non-log scale, giving a wrong aspect. See

Could it be that It would seem plots in log scale use a sampling done in the non-log scale?

scale...

Since plots only 200 plot points by default, the sampling in non-log scale means that for a log-scale plot, most plot points are near the end, and they are very scarce in the first 3/4 of the plot.

A workaround, as suggested in @Iguananaut's answer, is to use more plot points.

Using 800 plot points already gives a much smoother curve here:

sage: tau = RDF.pi()*2
sage: out2 = lambda r, c: lambda f: ~(1 + (tau*f*r*c)^2)
sage: plot(out2(15, 2.7e-9), (10, 500e6), scale='loglog', plot_points=800)
Launched png viewer for Graphics object consisting of 1 graphics primitive

There was a problem I thought looked similar: the x-range and y-range for a plot are chosen slightly wider than the actual range of x-values and y-values that occur in the plot, and sometimes in log scale it looks like this "slightly wider" is chosen in non-log scale, giving a wrong aspect. See