Convergence criterion

Exit of the loop over iterations is controlled by a convergence criterion, that is defined by four parameters ConvNormType, εconv, Lref, Fref, and Eref, in the step control parameter data section.

The incremental equations of motion of the system are written as K Δu = F, where K is the tangent stiffness matrix, Δu the incremental displacements, and F the out of balance forces. A ConvNormType should be selected from the following three types.

  • ConvNormType = DISPLACEMENT: The convergence norm is based on the incremental displacements; the convergence criterion is
    uT diag(K) Δu) / Lref ≤ εconv.
  • ConvNormType = FORCES: The convergence norm is based on the out of balance forces; the convergence criterion is
    FT [diag(K)]-1 ΔF) / Fref ≤ εconv.
  • ConvNormType = ENERGY_LIKE: the convergence norm is based on an energy like dot product; the convergence criterion is
    FT Δu) / Eref ≤ εconv.

The loop over iteration is exited when the selected convergence criterion is met. (Default values: ConvNormType = ENERGY_LIKE; Lref = 1.0; Fref = 1.0; εconv = 1.0 10-06).