Incorrect strain passed to UMAT in incremental driver for TriaxialUEq

[WaveHello]

For a linear elastic model (or when the state of the soil is in a linear elastic region), the mean stress and the volumetric strain are coupled. This means for undrained tests that use linear elastic material sections the mean stress cannot change because the volumetric strain is constrained to be zero. Incremental driver has an option to model undrained strain controlled triaxial problems but the strain increment (dstrain) that's passed to the material model only contains the forced strain. For example if dstrain should be:

dstrain = [-0.2, 0.4, -0.2, 0, 0, 0]

which would mean the volumetric strain would be constant as it's the sum of the first three terms. However, what's passed to the umat is

dstrain = [0, -0.4, 0, 0, 0, 0]

As the volumetric strain is no longer zero the mean stress changes. However, dstrain is overwritten with the correct value when output to the text file. This makes this bug kind of annoying to find.

[WaveHello]

This was a user error. I did something wrong including the UMAT in incremental driver. don't know what I did wrong at this time.

[WaveHello]

Meant to close the issue.