## Convergence criterion

Exit of the loop over iterations is controlled by a **convergence criterion**, that is defined by four parameters ** ConvNormType**,

*,*

**ε**_{conv}*,*

**L**_{ref}*, and*

**F**_{ref}*, in the step control parameter data section.*

**E**_{ref}The incremental equations of motion of the system are written as * K Δu = F*, where K is the tangent stiffness matrix,

*the incremental displacements, and*

**Δ**__u__*the out of balance forces. A*

__F__**should be selected from the following three types.**

*ConvNormType*-
: The convergence norm is*ConvNormType = DISPLACEMENT**based on the incremental displacements*; the convergence criterion is

**(Δ**__u__^{T}diag(K) Δ__u__) / L_{ref}≤ ε_{conv}. -
: The convergence norm is*ConvNormType = FORCES**based on the out of balance forces*; the convergence criterion is

**(Δ**__F__^{T}[diag(K)]^{-1}Δ__F__) / F_{ref}≤ ε_{conv}. -
: the convergence norm is*ConvNormType = ENERGY_LIKE**based on an energy like dot product*; the convergence criterion is

**(Δ**__F__^{T}Δ__u__) / E_{ref}≤ ε_{conv}.

The loop over iteration is exited when the selected convergence criterion is met. (*Default values:* ** ConvNormType** = ENERGY_LIKE;

*;*

**L**_{ref}= 1.0*;*

**F**_{ref}= 1.0*).*

**ε**_{conv}= 1.0 10^{-06}