$\newcommand{\Dev}{\operatorname{Dev}}$ $\newcommand{\dev}{\operatorname{dev}}$ $\newcommand{\grad}{\operatorname{grad}}$ $\newcommand{\divg}{\operatorname{div}}$ $\newcommand{\Ei}{\operatorname{Ei}}$ $\newcommand{\tr}{\operatorname{tr}}$

Although technically not a limitation of FEBio it is important that users are aware that in some cases you may get a different convergence history or sometimes even a slightly different answer when you run the same model twice on a multi-processor machine. This is caused by the fact that on multi-processor machines the same calculations can be executed in a different order and due to the accumulation of numerical round-off errors may result in slightly different answers. The type of problems that are mostly affected by this are problems that are close too being ill-conditioned. Also, problems that have many time steps or require many iterations for each time step may be affected by this.