Simulation with SINDy returns a straight line only

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Hi , I am Sayeed.
I am using SINDy method to predict Magnetoelectric sensor output . When I applied the SINDy-PI on my data it discovers the model closely (for example if I excite my sensor using a sinusoidal signal I get x' = cosx , that seems correct or close.) But when I fsimulate the model it always returns a straight line (I used Chirp and Sine signal to excite my sensors and in both cases I came up with a straight line.) It seems SINDy is simulatiing x'=x' in every case. How to get rid of that?

problem 2: I cant zoom in the figure I get after simulation to compare how well is the fit. But in Matlab it zooms well. Can anyone tell me How to solve this? I once accidentally got figures that can be zoomed but I can't reproduce it again.
I am new to coding . Any help would be appreciated.


In the simulated graph, The red area is actually a sine signal , due to the high sampling rate it appers so. If zoomed it can be seen on my screen. As this is just a screenshot , the zoom to see the sine wont be possible.