# Initial Conditions of FAST versus Simulink

**URL:** <https://forums.nlr.gov/t/initial-conditions-of-fast-versus-simulink/556>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [August 2, 2012, 11:52pm UTC](https://forums.nlr.gov/t/initial-conditions-of-fast-versus-simulink/556 "2012-08-02T23:52:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Layne.Clemen](https://avatars.discourse-cdn.com/v4/letter/l/7cd45c/32.png) [@Layne.Clemen](https://forums.nlr.gov/u/Layne.Clemen)\
**Post date:** [August 2, 2012, 11:52pm UTC](https://forums.nlr.gov/t/initial-conditions-of-fast-versus-simulink/556/1 "2012-08-02T23:52:23Z")

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I have implemented the controller for the NREL 5 MW in simulink and I am getting the same steady state outputs but the initial start up portion of the simulation, approximately 20-30 seconds depending on input type, is slightly different. It seems that the initial conditions are affecting the controller. What executes first when running FAST from simulink? Does the S-function execute first or does all of the control logic execute?