# Logscale on negative real axis
**URL:** https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814
**Category:** Visualization
**Tags:** makie
**Created:** [January 31, 2023, 9:41am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814 "2023-01-31T09:41:57Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@gvdeynde](https://discourse.julialang.org/u/gvdeynde)
#### Post date: [January 31, 2023, 9:41am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/1 "2023-01-31T09:41:57Z")
Hi all
I have a function, `foo(x)`, which is defined only on the negative real axis. The range is quite wide and I want to plot it in log-scale, say from x=-1.0e7 to x=-1.0e-7. How can I “transform” the axis in `Makie` to allow this “negative” logscale? I can transform y=-x by myself, of course, but then the plot is from +1.0e-7 to +1.0e+7, i.e. mirrored left-right… I cannot re-mirror it by setting the xlims (no output); I guess that the transform is flipping because of negative values in log scale.
---
### Author:  [@jules](https://discourse.julialang.org/u/jules)
#### Post date: [January 31, 2023, 10:03am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/2 "2023-01-31T10:03:09Z")
You can re-mirror by setting `ax.xreversed = true`? The tick labels will be positive of course, one could change that via formatting but it’s a little annoying I guess. Another option would be to add `negative_log` as an axis scale function. Here’s how you’d do that, it’s not really documented because it’s not something people often do. I’m hijacking the functionality for normal log ticks by running the tick finding on the positive mirror values and converting back.
```julia
neglog10(x) = log10(-x)
Makie.defaultlimits(::typeof(neglog10)) = (-100, -1)
Makie.defined_interval(::typeof(neglog10)) = Makie.OpenInterval(-Inf, 0.0)
Makie.inverse_transform(::typeof(neglog10)) = x -> -exp10(x)
function Makie.get_ticks(::Makie.Automatic, scale::typeof(neglog10),
any_formatter, vmin, vmax)
vals, labels = get_ticks(LogTicks(WilkinsonTicks(5, k_min = 3)), log10, any_formatter, -vmax, -vmin)
-vals, rich.("-", labels)
end
data = sort(-exp.(rand(-7..7, 1000)))
scatter(data, axis = (; yscale = neglog10))
```
---
### Author:  [@gvdeynde](https://discourse.julialang.org/u/gvdeynde)
#### Post date: [January 31, 2023, 10:42am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/3 "2023-01-31T10:42:01Z")
In my setup, I need to change
```julia
vals, labels = get_ticks(LogTicks(WilkinsonTicks(5, k_min = 3)), log10, any_formatter, -vmax, -vmin)
-vals, rich.("-", labels
```
to
```julia
vals, labels = Makie.get_ticks(LogTicks(WilkinsonTicks(5, k_min = 3)), log10, any_formatter, -vmax, -vmin)
-vals, rich.("-", labels
```
And sorry to nag, but the code doesn’t work for me when applied on the x-axis (using pure negative values, of course). Which is kind of weird…
---
### Author:  [@jules](https://discourse.julialang.org/u/jules)
#### Post date: [January 31, 2023, 10:44am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/4 "2023-01-31T10:44:05Z")
I don’t know, this works for me `scatter(data, data, axis = (; xscale = neglog10))`
---
### Author:  [@gvdeynde](https://discourse.julialang.org/u/gvdeynde)
#### Post date: [January 31, 2023, 10:47am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/5 "2023-01-31T10:47:08Z")
> [@jules](#):
>
> scatter(data, data, axis = (; xscale = neglog10))
Yes. That works for me as well. Weird. My bad. Thanks for the nifty solution!
---
### Author:  [@gvdeynde](https://discourse.julialang.org/u/gvdeynde)
#### Post date: [January 31, 2023, 10:58am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/6 "2023-01-31T10:58:29Z")
It seemed that my range is too wide (-1e7 to -1e-7)…
This works:
> pmin = -3
> pmax = 3
> x = sort(-(10.) .^ range(pmin,pmax, 1000))
> lines(x, x, axis = (; xscale = neglog10, yscale = neglog10))
but changing `pmin` to -4 or `pmax` to +4, gives no output (no warnings/errors either, just no output).
Do I need to manually set limits for the axis?
---
### Author:  [@jules](https://discourse.julialang.org/u/jules)
#### Post date: [January 31, 2023, 11:41am UTC](https://discourse.julialang.org/t/logscale-on-negative-real-axis/93814/7 "2023-01-31T11:41:12Z")
Hm yeah that is weird, I get
```julia
ERROR: Found invalid x-limits (-10000.0f0, 0.0f0) for scale neglog10 which is defined on the interval -Inf..0.0 (open)
```
seems like the float32 conversion lets the max value round up to 0, which is not allowed for log scale. There’s an open PR to fix such issues by switching to Float64, at least for CairoMakie.