You can try SYSP 901, 1 to only have 1 core being used for multi-threaded calculations.  To use all the cores, you can reset it with SYSP 901, 0.

Hi Roger,

None of the ZPL Keywords (or functions or variables) are case sensitive.  There is a ZPL pre-processor which converts all keywords, functions & variables to upper case and then the ZPL itself is run.  So, I would use caution with your above code if all you have changed is zrd2mat to ZRD2MAT.

What is most likely happening is based on the complexity of your ZRD file and how many other processes are opened, you’re getting lucky that the ZRD2MAT keyword is only using a single thread when calling the external MATFileGenerator.dll.  Since the MAT file format (binary -v7) has a complex data structure, the entire MAT file needs to be written at the same time OpticStudio by default chunks the ZRD file and reads/processes a ZRD using multiple threads.  So, the more complex (i.e., more rays) a ZRD file, the more threads OpticStudio will try to process the data and the more likely there will be issues writing the MAT file.

You can also turn off multi-threading by using the GUI if you don’t want to change your code (System Explorer > Advanced > Turn Off Threading):

Michael is correct that ZPL should NOT be case sensitive, but if that one keyword is, someone in Zemax development should have a look.

The ‘Turn off Threading’ and SYSP tricks were intended to test whether threading was the problem, and using them should only be for debugging.

The 2 in ZPL2MAT might be a problem as the vast majority of keywords do not have numbers in them.