# Distribution in Calibration

**URL:** <https://persalys.discourse.group/t/distribution-in-calibration/55>\
**Category:** Persalys usage\
**Created:** [April 29, 2021, 7:04am UTC](https://persalys.discourse.group/t/distribution-in-calibration/55 "2021-04-29T07:04:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cdurantin](https://yyz2.discourse-cdn.com/free1/user_avatar/persalys.discourse.group/cdurantin/32/19_2.png) [@cdurantin](https://persalys.discourse.group/u/cdurantin)\
**Post date:** [April 29, 2021, 7:04am UTC](https://persalys.discourse.group/t/distribution-in-calibration/55/1 "2021-04-29T07:04:58Z")

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Hello,

I am performing a test case study with Persalys and the only module I’m struggling with is Calibration.  
When I try to use BLUE or 3DVAR methods, I can’t change the standard deviation for the Calibration parameter, an error message is printed in red (see attached screenshot).  
Also I don’t see where I can define the covariance matrix of the output observations.  
My Persalys xml file is also uploaded. [Étude\_test.xml](https://persalys.discourse.group/uploads/short-url/zcxsGKZH086c4AMDERvq3IDDpxo.xml) (3.3 MB)

 ![PersalysBugCal](https://global.discourse-cdn.com/free1/uploads/persalys/original/1X/582b1de585f41142049b988102de3b78c5a26786.png)

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**Author:** ![mbaudin47](https://yyz2.discourse-cdn.com/free1/user_avatar/persalys.discourse.group/mbaudin47/32/137_2.png) [@mbaudin47](https://persalys.discourse.group/u/mbaudin47)\
**Post date:** [May 3, 2021, 9:15am UTC](https://persalys.discourse.group/t/distribution-in-calibration/55/2 "2021-05-03T09:15:19Z")

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Hi Cédric,

Welcome on this forum !

I was not able to load to the xml with my current version of Persalys: what version do you use?

According to the message, I would say that the physical model is not consistent with the observations selected from the data model. Notice that there are several kinds of variables in a calibration study:

- observed input variables, which are read from the data model, that is \boldsymbol{x},
- calibration input variables of the physical model, that is \boldsymbol{\theta},
- observed output variables, which are read from the data model, that is \boldsymbol{z}.

The physical model must be:

\boldsymbol{z} = h(\boldsymbol{x}, \boldsymbol{\theta})

and the data model must contain both \boldsymbol{x} and \boldsymbol{z}.

This is perhaps better explained at:  
[http://openturns.github.io/openturns/master/theory/data\_analysis/code\_calibration.html](http://openturns.github.io/openturns/master/theory/data_analysis/code_calibration.html)

In the meantime, I try to test in with another version and let you know if I can reproduce the bug.

Regards,

Michaël