# How to fix a parameter

**URL:** <https://discourse.pumas.ai/t/how-to-fix-a-parameter/711>\
**Category:** How-to\
**Created:** [June 25, 2022, 6:59am UTC](https://discourse.pumas.ai/t/how-to-fix-a-parameter/711 "2022-06-25T06:59:41Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Fate.A](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@Fate.A](https://discourse.pumas.ai/u/Fate.A)\
**Post date:** [June 25, 2022, 6:59am UTC](https://discourse.pumas.ai/t/how-to-fix-a-parameter/711/1 "2022-06-25T06:59:41Z")

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hello  
I’d like to fix a parameter (ka) in order to fit my model.  
how would one fix a parameter?  
thx

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<div class="post-metadata">

**Author:** ![vijay](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.pumas.ai/vijay/32/96_2.png) [@vijay](https://discourse.pumas.ai/u/vijay)\
**Post date:** [June 25, 2022, 8:20am UTC](https://discourse.pumas.ai/t/how-to-fix-a-parameter/711/2 "2022-06-25T08:20:12Z")

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hi -  
picking this up directly from the documentation here [Estimating Parameters of Pumas Models · Pumas](https://docs.pumas.ai/stable/basics/estimation/#Maximum-Likelihood-Estimation)

It is possible to fix one or more parameters of the fit by passing a `NamedTuple` as the `constantcoef` argument with keys and values corresponding to the names and values of the fixed parameters, e.g. `constantcoef=(σ=0.1,)`. Example syntax

```julia
myfit = fit(mymodel, drug_x_population, drug_x_parameters, Pumas.FOCE(),
            constantcoef = (tvcl = 4, ))

```