# Error concerning ipopt when using ATOM fmincon() in Scilab 2026

**URL:** <https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152>\
**Category:** Atoms packages\
**Created:** [May 21, 2026, 2:31pm UTC](https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152 "2026-05-21T14:31:08Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![vmagnin](https://yyz2.discourse-cdn.com/free1/user_avatar/scilab.discourse.group/vmagnin/32/1048_2.png) [@vmagnin](https://scilab.discourse.group/u/vmagnin)\
**Post date:** [May 21, 2026, 2:31pm UTC](https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152/1 "2026-05-21T14:31:08Z")

</div>

I need to use the ATOM [fmincon](https://atoms.scilab.org/toolboxes/fmincon). I have installed it in Fedora 44 both in Scilab 2026.0.1 and the latest Scilab 2026.1.0 (installed with the official .tar.xz),with its two dependencies via the command `atomsInstall("fmincon")`:

```auto
--> atomsGetInstalled()
fmincon 1.0.9 allusers SCI/contrib/fmincon/1.0.9 I
sci_ipopt 1.3.5 allusers SCI/contrib/sci_ipopt/1.3.5 A
apifun 0.4.3 allusers SCI/contrib/apifun/0.4.3 A

```

In order to learn `fmincon()`, I have downloaded the demos from its GitLab: [demos · master · scilab / forge / fmincont · GitLab](https://gitlab.com/scilab/forge/fmincont/-/tree/master/demos)

```auto
--> exec('/home/blabla/fmincont/demos/fmincon_hesspattern.sce', -1)
à la ligne 287 de la fonction fmincon_ipopt (/home/blabla/scilab-2026.1.0/share/scilab/contrib/fmincon/1.0.9/macros/fmincon/fmincon_ipopt.sci ligne 297 )
à la ligne 406 de la fonction fmincon ( /home/blabla/scilab-2026.1.0/share/scilab/contrib/fmincon/1.0.9/macros/fmincon/fmincon.sci ligne 418 )
à la ligne 45 du fichier exécuté /home/blabla/fmincont/demos/fmincon_hesspattern.sce

ipopt : Taille erronée de l'argument d'entrée #1 : une seule structure attendue.

```

I have tried several other demos, and obtain always the same error about `ipopt`.

---

<div class="post-metadata">

**Author:** ![mottelet](https://yyz2.discourse-cdn.com/free1/user_avatar/scilab.discourse.group/mottelet/32/13_2.png) [@mottelet](https://scilab.discourse.group/u/mottelet)\
**Post date:** [May 22, 2026, 7:14am UTC](https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152/2 "2026-05-22T07:14:03Z")

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Hello,

I updated sci\_ipopt yesterday evening, you should be fine with

```auto
atomsRemove fmincon

```

quit and relaunch Scilab, then

```auto
atomsSystemUpdate
atomsInstall fmincon
atomsLoad fmincon

```

S.

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<div class="post-metadata">

**Author:** ![vmagnin](https://yyz2.discourse-cdn.com/free1/user_avatar/scilab.discourse.group/vmagnin/32/1048_2.png) [@vmagnin](https://scilab.discourse.group/u/vmagnin)\
**Post date:** [May 22, 2026, 7:49am UTC](https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152/3 "2026-05-22T07:49:10Z")

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Thanks a lot @mottelet ,  
I can confirm it now works in Scilab 2026.1.0! I have tested successfully several demos from the `fmincon` GitLab sources.  
Thanks for your efforts maintaining it.  
V.

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<div class="post-metadata">

**Author:** ![mottelet](https://yyz2.discourse-cdn.com/free1/user_avatar/scilab.discourse.group/mottelet/32/13_2.png) [@mottelet](https://scilab.discourse.group/u/mottelet)\
**Post date:** [May 22, 2026, 7:53am UTC](https://scilab.discourse.group/t/error-concerning-ipopt-when-using-atom-fmincon-in-scilab-2026/1152/4 "2026-05-22T07:53:50Z")

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Thanks for using fmincon. If you didn’t already run this example : [https://scilab.discourse.group/t/large-scale-nonlinear-optimization-with-fmincon-in-scilab-vs-matlab](https://scilab.discourse.group/t/large-scale-nonlinear-optimization-with-fmincon-in-scilab-vs-matlab), I encourage you to do so, as it shows that fmincon+IPopt outperforms Matlab’s fmincon.

S.