Forum Discussion
How do you get an R script to locate the Xpress license?
I just installed Xpress optimizer (on Linux MInt) and tried out the first_lp_problem.R example. The call to xprs_loadproblemdata() failed with the message "The license file was not found in '.'." Note that the XPAUTH_PATH environment variable is correctly set. Changing the working directory in the R session to the Xpress bin directory fixed the problem, but it is not practical to require an R session be running in that directory in order to access Xpress.
What is the correct way to get the xpress R library to find the license file?
Thanks.
3 Replies
Answering myself (seldom a good sign): This is actually an RStudio problem, not an Xpress issue. If I run R in a terminal and source the .R file, it runs fine. The error only occurs when I run the example in the RStudio IDE (either by opening the .R file in the editor or by sourcing it in the console). So I'll ask in the Posit community.
In case any other Xpress users trip over this, I found a fix. The problem is that when RStudio is run, it does not see the bash environment variables. I created a text file named ".Renviron" in my home directory (one did not already exist) and added the line "XPAUTH_PATH=/home/paul/Software/XpressMP/bin/xpauth.xpr". This means that RStudio (and the R session it is using) can see the license variable. The other Xpress-related environment variables are not loaded but apparently are not needed.
Thanks for posting the answer yourself and helping other users to avoid this common pitfall between R and RStudio. In RStudio you can verify that the environment variable is actually set by executing
Sys.getenv("XPAUTH_PATH")from inside the interactive RStudio terminal. If this returns an empty string, follow Paul's recipe and make sure that RStudio is launched with a valid .Renviron initialization.
