Resolving Error Related to Data Reader Routine while Calculating Difference in Variable

When trying to calculate the difference between a variable at different timesteps I get the error: Specified function requires a data reader routine that is not implemented.

The error message "Specified function requires a data reader routine that is not implemented" can appear when an user tries to calculate the difference of a variable between two different timesteps in the form:

myDiff = myVar – myVar{0}

where the current step solution is compared with the first timestep solution.

The error is connected to how Ansys EnSight tool handles the transient data. In order to avoid the issue, one can do instead

myVarT0 = myVar{0}
myDiff = myVar - myVarT0

In this way the calculation is also more efficient since myVar{0} is stored and EnSight would not have to load the first time-step data for every successive calculation in different instants in time.

Similar considerations apply to the case below

myDiff = myVar{8} - myVar{2}

that can be replaced as

var1 = myVar{8}
var2 = myVar{2}
myDiff = var1 - var2