On Mon, Oct 17, 2016 at 03:01:11AM +0200, Alex van den Bogaerdt wrote: > > What I want to achieve (and what I think those other proponents also > > had in mind) is that I essentially have some of my data mirrored at > > the x-axis for better readability (don't draw two values on top of > > each other). > > > > For example I plot outgoing packets on my network as a positive values > > while I plot the incoming packets via CDEF:output=0,outputx,- as > > negative values. So the outgoing rate is shown above the x-axis and > > the incoming rate below the x-axis. > > So, what you want to show is the outcome of a normal logaritmic function, > but mirrored. Instead of a new function...

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Basically, yes, but because of the y axis I think I need some special logic in rrdgraph (see below). > > To tame network spikes somewhat I want to change the graph mode to > > logarithmic. This works for the positive values, but the negative > > values simply vanish. I just want the same transormation that happens > > to the positive values applied 'mirrored' the the negative values. > > > > Think of something like a "display-logarithm" function defined like > > this: > > > > > > double disp_log(double y) > > { > > if (y == 0) { > > return 0; > > } else if (y > 0) { > > return log(y); > > } else { > > return -log(-y); > > } > > } > > > > > > While "-log(-y)" might look weird in a mathematical context I think that > > it makes sense in describing "do the same as for positive values, only > > in the other direction". > > ... can't you just use CDEF:mirrored=logresult,-1,* ? > Or am I missing something ? This would indeed give me the correct results and would draw a correct graph, but the y axis grid would not be logarithmic: If I put the values "1000" and "-1000" into a CDEF using normal and 'mirrored' LOG, I'll graph the values "3" and "-3". The y grid will propably autoscale to "-10 … 10" and show my values as "3" and "-3" instead of "1000" and "-1000". When I use --logarithmic, the positive values are also LOGed, but the y axis will be scaled logarithmic as well, so the y axis will show "1000" (or "10e3" or "1k") next to the graph value. If I could get a logarithmic y axis without using --logarithmic (for both positive and negative values), using LOG in a CDEF would indeed be a solution. Regards Christian -- ....Christian.Garbs....................................https://www.cgarbs.de "Die Berühmtheit mancher Zeitgenossen hängt mit der Blödheit der Bewunderer zusammen." -- Heiner Geissler _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users