How to reference a parameter to a DAX function ?

It is possible through multiple steps, 2 possibilites exist depending on the volume of your tables 

1. Use powerquery and merge your table with the parameter. The parameter will repeat on every line. You can then use it through calculations directly in powerquery, or with DAX. 

Parameter 1 : 0,5

Vendor

John 1
John 2
John 3

With an outerleft join, 

2. If your data has high volume, reference the parameter on your fact table using power query. like in example 1 

In your 2nd table, use DAX and reference the value 

LOOKUPVALUE( 'Infotable'[Parameter1], Info table[Vendor name]>, 'Currenttable'[Vendor] )

This will return the parameter 0,5 to every line, and can then be used for calculations using DAX