I get an error that I don't understand when I try to replace expressions into the Complex Ginzburg Landau equation. I got the following error
Coefficient::ivar: 1 is not a valid variable. >> q M a n i p u l a t e ` D u m p `
I would like to replace the expressions and then to collect terms in scales of $\epsilon$
I attach here the notebook for the equation that I have written, I am new to Mathematica so any hint will be great!
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