Both PLAXIS 2D and PLAXIS 3D programs allow for multi-core calculations and are Windows 64-bit applications. This is possible when using a PLAXIS 2D/3D Advanced or PLAXIS 2D/3D Ultimate license tier.
For more information on licenses, check the article on PLAXIS Licenses.

This can be beneficial to complex calculations that involve the computation of parallel phases as the available computer resources can be used in an efficient way and result in a faster calculation time for the whole project.

How to perform parallel phase calculations

With PLAXIS it is possible to have multiple and independent phases that can be run in parallel, provided that they are starting from the same parent phase and the parent phase is already successfully calculated.
This means that when you have a single list of consecutive phases, parallel calculations cannot be utilized.

To achieve parallel calculations, the phase property Max cores to use needs to be configured appropriately. This property can be found in the Phases window.

This number specifies how many cores will be used per phase calculation. If the number is larger than the number of available cores in your computer, the calculation will only use the available physical cores. For example, on a quad-core PC using the default of 256 Max cores to use, you will use 4 cores for the phase calculation in a multi-core calculation.

Picture 1. PLAXIS configuration of phases and Max cores to use option in the Phases window Spreadsheet view

Note that the calculation will only start with a phase when there are enough CPU cores available to launch one.

Assuming an octa-core (8) computer with a project with multiple and independent phases, depending on the setup of the Max cores to use in the calculation, the following may happen:

• Set to the maximum number of cores (8 or more):
  One phase at a time will be calculated regardless of having parallel phases.
  When the number of maximum cores to be used for a phase is set to a number equal to or greater than the number of available CPU cores, it will use the maximum number of cores per phase, leaving no room for any additional calculation to be run at the same time.
• Set to 1 core per phase:
  Parallel phase calculation is possible.
  When you limit the number of cores per phase to one [1], it is possible to calculate independent phases at the same time, provided that they are starting from the same parent phase and the parent phase is already successfully calculated.
• Set to 2 cores per phase:
  When you limit all your phases to only use 2 cores, up to a maximum of 4 independent phases can be calculated at the same time.
  Note that in this specific case, PLAXIS will leave no cores free for other programs in your computer to use.
• Set to 3 cores per phase:
  When you limit all your phases to only using 3 cores, only the first two parallel phases will run on 3 cores. The remaining phases will wait until 3 cores become available and used in the calculations.
  Note that in this specific case, during the calculations, PLAXIS will leave 2 cores free for other programs in your computer to use.

Available solvers in PLAXIS

With PLAXIS 3D it is possible to choose different solver types to solve the matrix of equations: Picos (default), Pardiso and Classic.
Note that for PLAXIS 2D only Picos solver is available.

• Picos (multicore iterative). It stands for Plaxis Iterative Concurrent Solver library. Picos is an efficient iterative solver that solves the system of equations in parallel on multi-core processors. It is generally the fastest way to perform calculations.
• Pardiso (multicore direct). It stands for Parallel Sparse Direct Solver. Pardiso is a direct solver that solves the system of equations in parallel on multi-core processors. It is generally the most robust way to solve equations, but it has also the highest memory consumption.
• Classic (single core iterative). This is the iterative solver that solves the system of equations using only a single core on the processor.

Specifically, for PLAXIS 3D, the Pardiso solver is limited to a maximum of 500,000 (active) elements. When there is not enough memory available to use the Pardiso solver or this element limit has been reached, it will switch to the Picos solver.
For more information about these solvers, please refer to the Reference Manual.