doubt on coding functions

[debasismpt]

can anybody explain me in detail what is the work of commitstate(),reverttolastcommit(),revertTostart() functions in opensees coding.

[fmk]

in OpenSees during each nonlinear analysis step the solution algorithm moves the model through many trial steps in an attempt to find a solution that meets the convergence criteria set for that analysis step. if the analysis step works, i.e. convergence is achieved at the last trial step, the analysis step stops and the commitState() is invoked on the elements and materials telling them that the last step was on the solution path. If the solution algorithm fails, the analysis stops and the model is returned to the last point on the solution path for which convergence was achieved (the last time the commitState was called). For this to happen all elements and materials are called with the revertToLastCommit().

if revertToStart is invoked the elements and materials are supposed to go back to their original undeformed configuaration.