Re: [Gnuplot-info] logscale and autoscale improvement (was logscale and manual range setting?)

[Jim K. <je...@kl...>]

Hans-Bernhard Broeker wrote:
> Jim Kleckner wrote:
> 
>> It would be nice to have the autoscale logic be able to
>> handle the scaling to waste less space, I think.  
> 
> 
> The case you stumbled on is quite particular.  The data yrange is
> [1-epsilon:4.0]  This drives autoscaling for log axis exactly into its 
> worst-case scenario.
> 
> 1) the input range is scarcely one decade long
> 2) it's positioned uncomfortably, with one end point scarcely below a
>    natural tic position.
> 3) it's a logarithmic axis.
> 
> Item 2) means that the autoscaled range will be extended beyond that
> power-of-ten.  Throwing data points off the plot (like 'set yrange 
> [1:10]' does it in this case), is strictly a non-option for the 
> automatic behaviour of gnuplot.  You can turn off this extension, at the 
> risk of getting rather ugly ranges.  See "help autoscale"; the 'fix' 
> options.
> 
> Item 3) means that the extension cannot currently be shorter than one
> full unit in logarithm (i.e. a factor of 10) --- that's why the 
> autoscaled range ends up being [0.1:10].  The core limitation here is 
> that gnuplot still has no way ofcontinuously changing from the only 
> sensible ticking pattern for long log axes (labelled, graphically 
> equidistant major tics, unlabelled, arithmetically equidistant tics in 
> between) to the only sensible one for very short axes (labelled, 
> arithmetically equidistant tics).
> 
> The fact that the additional is perceived to be creating such a huge
> "waste" of plot space is because of item 1).  In the essence, you're in 
> violation of an old lemma of scientific plotting: "He who uses a 
> logarithmic axis spanning less than two decades is rather probably 
> trying to brush some embarrasing detail under the carpet."

It would be great if all of my financial returns exceeded a decade or 
two! :)  Unfortunately, the natural way to look at compounded returns is 
logarithmic and the noisy nature of the information can cause a dip 
below the starting value giving an extra decade at the bottom end and 
sometimes just above a decade at the top end.

>> How hard do you think it would be to start/end the axis
>> on a minitic rather than a major tic if too large a
>> fraction of the range is wasted?
> 
> 
> Starting the axis on a minitic is IMHO not the right solution.  Lifting 
> the limitation that in log axes only at integer powers of the base can 
> currently be major tics is what really needs tackling.  While at it, 
> other axis re-mappings than pow()/log() should be made possible.
> 
> Unfortunately, that'd end up in having to essentially re-write the 
> entire autoticking stuff from scratch.  James Van Zandt made a proposal 
> for that a long time ago, but it never made it into serious discussion, 
> let alone the CVS code.

It sounds like perhaps a function on the outside to detect this 
particular situation and set the manual range is the way to go.

Many thanks for your insight.

Jim