Formula Node Variables Not Maintaining Values in LabVIEW 2019

Updated Jul 3, 2020

Reported In

Software

  • LabVIEW

Issue Details

After upgrading my code to LabVIEW 2019 I am noticing that certain variables coming from my formula node are not updating properly when the code inside runs multiple times.

Why is this happening?
How do change my VI so this doesn't happen?

Solution

This is caused by a behavior change in LabVIEW 2019 related to variable initialization in formula nodes.

In prior versions, the variables would retain the value after the formula node runs but this was removed as it introduced additional unexpected behaviors in larger applications.

In LabVIEW 2019, the variables created inside the formula node can retain their value if you use a feedback node to maintain the value by using it between an input and an output. Below is an image detailing this architecture.