Re: [Gnuplot-info] Bugs? 1) Grid ticks in logscale incorrect when range above 1e6+1 and 2) also not plotted completely

[Ethan M. <eam...@gm...>]

There is no bug here - you are fighting the limits of floating point
precision.
Consider the final steps that are sampled as x approaches 10000.
For linear  sampling in steps of 100

f(9800)   is 490000.000000002
f(9900)   is 990000.00000001
f(10000) is inf   (divide by zero at IEEE floating precision)

So f(9900) is the last point that shows on the plot, and that value is less
than the y range you have chosen.  The function reaches ymax (10^7) at
f(9990.)
To catch that on your plot you must sample finely enough to distinguish
9990 from 10000.

And that's for linear sampling. In logscale the sampling must be even finer.
The program selects even samples along the x axis (even spacing on log(x)).
So most of the samples are at low values of x.

On Sun, Jul 31, 2016 at 5:16 AM, D <dcm...@we...> wrote:

> Thanks. I had to 'set sample' to 500000 for gnuplot to plot the whole line
> (slightly different xy range and the line goes to the bottom). Works in
> linear mode without the need for any 'set sample', wonder why the log mode
> requires that at all. Maybe you should fix that for v5.1 too.
>
>
> On 29.07.2016 20:52, Ethan Merritt wrote:
>
> 1)   version 5.0:
>       set mxtics 10                  # see "help set mxtics"
>       set mytics 10
>
>      version 5.1
>       currently a bug.  thanks for the report
>
> 2) set sample 10000
> Or else define the functions as parametric so that the sample is
> independent of the x/y precision.
> But increasing the number of samples is easier.
>
> On Fri, Jul 29, 2016 at 11:28 AM, D <dcm...@we...> wrote:
>
>> Hi, using:
>>
>> set terminal pngcairo truecolor enhanced font "arial,11" fontscale 1.0
>> size 1000,1000
>> set output "test.png"
>>
>> set log xy
>> #set logscale xy
>>
>> set xrange [100:1e7]
>> set yrange [100:1e7]
>>
>> set grid xtics ytics mxtics mytics lt 0 lw 1 lc rgb "#000000"
>>
>> f(x)  = x/   (1-0.0001*x)
>> fi(x) = x/(1/(1-0.0001*x))
>> g(x)  = x/   (1-0.0000001*x)
>> gi(x) = x/(1/(1-0.0000001*x))
>> id(x) = x
>>
>> plot f(x)  lt 2 lc rgb "#ff0000" lw 1 , \
>>       fi(x)  lt 2 lc rgb "#ff0000" lw 1  , \
>>       g(x)  lt 2 lc rgb "#ff0000" lw 1  , \
>>       gi(x)  lt 2 lc rgb "#ff0000" lw 1  , \
>>       id(x) dashtype 2 lc rgb "#000000" lw 1
>>
>> 1) the grid tick lines look either incorrect or at least not to what
>> they look up to [100:1e6]. How can I make them work with [100:1e7] ?
>> 2) the plot of the lines does neither go to the bottom (fi,gi), nor to
>> the top (f,g), as expected. How to fix?
>>
>>
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>
>