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Rick
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Why is their an offset when I intergrate a simple sin(1*x) in simulink using the (1/s) block?

Asked by Rick
on 10 Sep 2013
Their seems to be a -1 offset when I intergrate a sin(x) signal using a 1/s block. the sin(x) goes from -1 to 1 and the resulting intergation goes from 0 to 2? Is their a paramater i'm missing?

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1 Answer

Answer by Ryan G
on 10 Sep 2013

You need to set the initial condition of the integrator. I believe I cover this a bit in the intro to simulink webinar. This should help you ramp up if you're just getting started.

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I dont think this is the problem. The integral of sin(x) is -cos(x) as for the intial condition at t=0, sin(0)=0. In the 1/s block i set the itial condtion to be internal =0 and the result is still a cos(x) going from 0 to 2. My set up is simple I have a sin(x) going into a 1/s bock and I plot the two vs each other.
You're thinking of the solution analytically instead of numerically. The integral block only receives a value. It doesn't know if the value came from a sin , cos or a constant.
For example: At time t= 0 that value is into the integrator 0, time t=0.1 that value is sin(0.1)=0.0998 and the previous state (t=0) is 0. It will then integrate between those inputs using deltaT=0.1 with an IC of 0.
The time step changes dynamically based on the ODE45 (solver) algorithm tolerances.

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