Does anyone know how ABAQUS calculate ALLCD (viscoelastic energy dissipation)

Hi, 

I am doing some study with viscoelastic energy dissipation. I have a basic question for ABAQUS. 

In ABAQUS, I notice there is a function to calculate Energy dissipated by creep, swelling, and viscoelasticity (ALLCD). You are able to plot energy change with time. 

But want to know how ABAQUS calculates energy dissipation with time? What equation does it use?

I checked the textbook, when you need to calculate energy dissipation, you need to have at least one complete loading and unloading cycle. Then you use the integration area of loading/unloading curve to calculate energy. If the cycle is not completed, how do you calculate the energy? What is the equation to be used? 

Thank you advance for any answer or ideas.