# Why is the margin() function returning NaN?
**URL:** https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561
**Category:** Modelling & Simulations
**Tags:** question, package, controlsystems
**Created:** [June 2, 2025, 2:08pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561 "2025-06-02T14:08:01Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [June 2, 2025, 2:08pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/1 "2025-06-02T14:08:01Z")
I have the following linear state space system for 8 m/s wind:
```julia
julia> @time include("mwes/mwe_06.jl")
StateSpace{Continuous, Float64}
A =
0.0 0.0 0.217328
0.0 -142.50000000000003 -0.16245000000000004
0.0 0.0 -135.5115580754543
B =
0.0
0.0
77363.88168172735
C =
0.125 0.5 0.000608
D =
0.0
Continuous-time state-space model
```
Why does the function `margin` return NaN`
```julia
[Info: Gain margin: [NaN;;], Phase margin: [Inf;;], Gain crossover frequency: [14.923313891148691;;], Phase crossover frequency: [85.15256672572397;;]
StateSpace{Continuous, Float64}
```
The bode plot looks like this (this are two plots in one, one for 8 and one for 9 m/s wind)
---
### Author:  [@hexaeder](https://discourse.julialang.org/u/hexaeder)
#### Post date: [June 2, 2025, 2:20pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/2 "2025-06-02T14:20:24Z")
Gain margin is the gain at the frequency where your system crosses -180 degree. If your system never reaches that point, what result do you expect?
---
### Author:  [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [June 2, 2025, 2:32pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/3 "2025-06-02T14:32:24Z")
Please note, your printout
```julia
[Info: Gain margin: [NaN;;], Phase margin: [Inf;;], Gain crossover frequency: [14.923313891148691;;], Phase crossover frequency: [85.15256672572397;;]
```
is wrong, the phase margin is not `Inf`, you have confused phase margin and one of the frequencies
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [June 2, 2025, 2:48pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/4 "2025-06-02T14:48:30Z")
```julia
julia> margin(sys)
(wgm = [NaN;;], gm = [Inf;;], wpm = [16.691123499256943;;], pm = [80.97336203179722;;])
```
The function `diskmargin` from RobustAndOptimalControl gives a better output:
```julia
julia> diskmargin(sys)
Disk margin with:
Margin: 1.6377470230519808
Frequency: 27.113978155105443 rad/s, 4.3153236502707 Hz
Gain margins: [0.09958168466703816, 10.042007256089361]
Phase margin: 78.62627648625572
Delay margin: 0.050611806036664694 s
Skew: 0
Worst-case perturbation: 0.41321232142013375 - 1.7377816567466957im
```
But shouldn’t the function `margin` also work?
I understand the gain margins and phase and delay margin. But what is the meaning of “Margin: 1.63…” here?
---
### Author:  [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [June 2, 2025, 3:04pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/5 "2025-06-02T15:04:01Z")
> [@ufechner7](#):
>
> The function `diskmargin` from RobustAndOptimalControl gives a better output:
> [@ufechner7](#):
>
> But shouldn’t the function `margin` also work?
The diskmargins are defined differently, the traditional gain margin is truly not defined here so there is no problem with the output of the `margin` function.
> [@ufechner7](#):
>
> But what is the meaning of “Margin: 1.63…” here?
This is the diskmargin from which the other numbers are derived. See the paper cited in the docstring if you want to learn more.
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [June 2, 2025, 3:13pm UTC](https://discourse.julialang.org/t/why-is-the-margin-function-returning-nan/129561/6 "2025-06-02T15:13:51Z")
> [@baggepinnen](#):
>
> This is the diskmargin from which the other numbers are derived. See the paper cited in the docstring if you want to learn more.
Thank you so much!