I am not sure why you used a cascade forward net. That net has no feedack loops.
The generating equations indicate that a narxnet is more appropriate.
Is u(k)+ *0.3*u(k) a misprint? Should the latter be u(k-1)?
When you change to a narxnet, check the significant values (>0.21) of the crosscorrelation function nncorr(U,Y,N-1)and the autocorrelation function nncorr(Y,Y,N-1) to determine good values for the delays. The capitals indicate zscore transformations (i.e., U = zscore(u), etc).
Also change the divide function from dividerand (destroys u-y and y-y correlations) to either 'divideblock' or another choice.
As for your CFnet, you have 2 hidden layers with 30 nodes resulting in Nw = (1+1)*20+(20+1)*10+(10+1)*1 = 261 weights. A narxnet will probably need fewer hidden nodes and weights.
Hope this helps.
Thank you for accepting my answer.
Greg
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