# Restart failures (\*DYNAMIC) **URL:** \ **Category:** Uncategorized\ **Created:** [June 14, 2021, 7:59pm UTC](https://calculix.discourse.group/t/restart-failures-dynamic/623 "2021-06-14T19:59:06Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![vollmerb](https://avatars.discourse-cdn.com/v4/letter/v/90db22/32.png) [@vollmerb](https://calculix.discourse.group/u/vollmerb)\ **Post date:** [June 14, 2021, 7:59pm UTC](https://calculix.discourse.group/t/restart-failures-dynamic/623/1 "2021-06-14T19:59:06Z")
I am trying to restart a dynamic structural simulation in CalculiX, but the results upon restart do not agree with a non-restart run. For example, running for 20 steps as the “correct” solution, then running for 10 steps, and restarting to run for 10 more. I have tried combinations of (\*DYNAMIC,DIRECT), (\*DYNAMIC,DIRECT,EXPLICIT), NLGEOM, constant \*CLOAD, and variable \*CLOAD amplitude. I get the same results across multiple CCX versions (CCX\_2.10, CCX\_2.11, and CCX\_2.16). The restart itself does not fail, but it does produce a result inconsistent with the non-restart “correct” solution (i.e. y-displacement of node 2302 at t=0.02 should be 9.644763E-02 but if restarted at t=0.01 and run to 0.02 gives 9.644786E-02). Has anyone else come across this problem before? ---
**Author:** ![jbr](https://avatars.discourse-cdn.com/v4/letter/j/ecccb3/32.png) [@jbr](https://calculix.discourse.group/u/jbr)\ **Post date:** [June 15, 2021, 3:50am UTC](https://calculix.discourse.group/t/restart-failures-dynamic/623/2 "2021-06-15T03:50:39Z")
Hi @vollmerb, the numbers seem pretty close for a numerical solution. Assuming the non-restart is correct, then is a relative error in the displacement of about 2.385E-4%. ---
**Author:** ![vollmerb](https://avatars.discourse-cdn.com/v4/letter/v/90db22/32.png) [@vollmerb](https://calculix.discourse.group/u/vollmerb)\ **Post date:** [June 15, 2021, 4:08am UTC](https://calculix.discourse.group/t/restart-failures-dynamic/623/3 "2021-06-15T04:08:08Z")
Hi @jbr , I agree the error is small and possibly negligible in some cases (other setups I have tried gave ~0.05% error). However if the restart is implemented correctly I would expect exact agreement between the two. This leads me to think either I am applying the restart incorrectly or there is a bug in the CCX restart feature. ---
**Author:** ![vollmerb](https://avatars.discourse-cdn.com/v4/letter/v/90db22/32.png) [@vollmerb](https://calculix.discourse.group/u/vollmerb)\ **Post date:** [July 20, 2021, 7:41pm UTC](https://calculix.discourse.group/t/restart-failures-dynamic/623/4 "2021-07-20T19:41:05Z")
Update: There is a bug in the CCX restart feature where the acceleration going into the prediction() step is incorrect on a restart. I was able to fix this by adding acceleration read/write to the restarts and replacing acceleration and velocity before the prediction evaluation (on the first iteration only). The velocities need to be replaced due to a results evaluation on restart which is not present in a non-restarted continued iteration.