# Differential Equation Log Plot

**URL:** https://discourse.julialang.org/t/differential-equation-log-plot/123435
**Category:** Visualization
**Tags:** plotting, diffeq
**Created:** [December 4, 2024, 4:45am UTC](https://discourse.julialang.org/t/differential-equation-log-plot/123435 "2024-12-04T04:45:47Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![TheLazyFarmer](https://avatars.discourse-cdn.com/v4/letter/t/87869e/32.png) [@TheLazyFarmer](https://discourse.julialang.org/u/TheLazyFarmer)
#### Post date: [December 4, 2024, 4:45am UTC](https://discourse.julialang.org/t/differential-equation-log-plot/123435/1 "2024-12-04T04:45:47Z")

</div>

Hello,

I have some values from a differential equation I solved, I am trying to plot the y-axis as a logarithmic. However, I am unsure how to go about this approach:

For reference, I have this example solution from an ODE:

```julia
4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 0.0
 -1.0 -1.0 -1.0 0.0 0.0
 -1.0 -1.0 0.0 0.0 0.0
  6.022e23 0.0 0.0 0.0 0.0

4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 0.0
 -1.0 -1.0 -1.0 9.89029e-11 1.90176e-17
 -1.0 -1.0 1681.92 0.00290038 1.72268e-10
  6.022e23 2.86406e17 4.22592e10 12482.0 0.000225923

4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 8.82245e-23
 -1.0 -1.0 -1.0 3.17651e-9 1.01677e-15
 -1.0 -1.0 13455.3 0.046406 5.53283e-9
  6.02199e23 5.72812e17 1.69037e11 99855.6 0.00361477

4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 2.74788e-21
 -1.0 -1.0 -1.0 2.40525e-8 1.34756e-14
 -1.0 -1.0 45411.7 0.23493 4.18945e-8
  6.02199e23 8.59217e17 3.80332e11 3.37012e5 0.0182998

4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 2.03916e-20
 -1.0 -1.0 -1.0 1.01311e-7 7.5085e-14
 -1.0 -1.0 1.07642e5 0.742494 1.76463e-7
  6.02199e23 1.14562e18 6.76145e11 7.98843e5 0.0578362

4×5 Matrix{Float64}:
 -1.0 -1.0 -1.0 -1.0 1.00515e-19
 -1.0 -1.0 -1.0 3.0907e-7 2.88244e-13
 -1.0 -1.0 2.10239e5 1.81273 5.38336e-7
  6.02199e23 1.43203e18 1.05648e12 1.56024e6 0.141202

```

I have made a function to acquire only the indices which are positive (IE: The -1’s are skipped), so I have this statement to try and create my plot.

```julia
plot(sol, idxs = plottingIndices, ylims = (0, 6.022e23), xlims = (0, tspan_end), yscale=:log10)

```

However, I am confused how exactly to proceed from here. Every time I try to plot with this, I receive issues due to the 0s and -1s from the initial state of the array.

```julia
Warning: Invalid negative or zero value 0.0 found at series index 1 for log10 based yscale
Warning: Invalid negative or zero value -1.0 found at series index 1 for log10 based yscale

```

If anyone has any ideas how to solve this issue, I would greatly appreciate it!

---

<div class="post-metadata">

### Author: ![Sahil\_Khan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sahil_khan/32/47573_2.png) [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)
#### Post date: [December 4, 2024, 8:21am UTC](https://discourse.julialang.org/t/differential-equation-log-plot/123435/2 "2024-12-04T08:21:21Z")

</div>

Avoid 0 in limit. So, you are giving `ylim = (0, 6.022e23)` and want to apply `yaxis = :log10`. These both together are cause of issue because value of ‘log(0)’ is not defined. To solve it, you can rather give `ylim = (z, 6.022e23)` where z is some non zeros small value (around lowest value in your data).

Similarly for negative values, it will go in complex space.