# How to add parameters to a scripted similarity?
**URL:** https://discuss.elastic.co/t/how-to-add-parameters-to-a-scripted-similarity/317731
**Category:** Elasticsearch
**Tags:** painless
**Created:** [October 29, 2022, 2:51pm UTC](https://discuss.elastic.co/t/how-to-add-parameters-to-a-scripted-similarity/317731 "2022-10-29T14:51:59Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@fsanzestevez](https://discuss.elastic.co/u/fsanzestevez)
#### Post date: [October 29, 2022, 2:51pm UTC](https://discuss.elastic.co/t/how-to-add-parameters-to-a-scripted-similarity/317731/1 "2022-10-29T14:51:59Z")
I'm trying to make a parametrized scripted similarity function but I can't get it to work.
I have created the script and have it stored.
However, when I try to implement it in the similarity score, I keep getting errors because of the symbol [params].
^ I know my script looks very similar to BM25, but I need to parametrized certain values during the query.
```auto
{
"error" : {
"root_cause" : [
{
"type" : "script_exception",
"reason" : "compile error",
"script_stack" : [
"... f = doc.freq/(doc.freq + params['k1'] * (1 - param ...",
" ^---- HERE"
],
"script" : "double boost = 2.2 * doc.freq; double tf = doc.freq/(doc.freq + params['k1'] * (1 - params['b'] + params['b'] * field('dl_avgdl'))); double idf = Math.log(1 + ((params['docs_count'] - term.docfreq + 0.5)/(term.docFreq + 0.5))); return query.boost * tf * idf * norm;",
"lang" : "painless",
"position" : {
"offset" : 64,
"start" : 39,
"end" : 89
}
}
],
"type" : "script_exception",
"reason" : "compile error",
"script_stack" : [
"... f = doc.freq/(doc.freq + params['k1'] * (1 - param ...",
" ^---- HERE"
],
"script" : "double boost = 2.2 * doc.freq; double tf = doc.freq/(doc.freq + params['k1'] * (1 - params['b'] + params['b'] * field('dl_avgdl'))); double idf = Math.log(1 + ((params['docs_count'] - term.docfreq + 0.5)/(term.docFreq + 0.5))); return query.boost * tf * idf * norm;",
"lang" : "painless",
"position" : {
"offset" : 64,
"start" : 39,
"end" : 89
},
"caused_by" : {
"type" : "illegal_argument_exception",
"reason" : "cannot resolve symbol [params]"
}
},
"status" : 400
}
```
Is this possible to do with Elasticsearch 8.1?
---
### Author:  [@stu](https://discuss.elastic.co/u/stu)
#### Post date: [October 31, 2022, 1:29pm UTC](https://discuss.elastic.co/t/how-to-add-parameters-to-a-scripted-similarity/317731/2 "2022-10-31T13:29:48Z")
Hi @fsanzestevez, unfortunately `params` is not available for similarity scripts. So the script will need to embed the constants.
See the [similarity context docs](https://www.elastic.co/guide/en/elasticsearch/painless/current/painless-similarity-context.html) for all the variables available to similarity scripts.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [November 28, 2022, 1:30pm UTC](https://discuss.elastic.co/t/how-to-add-parameters-to-a-scripted-similarity/317731/3 "2022-11-28T13:30:13Z")
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