Question: How to treat differentiation as an operator

Hello there, 

Would you tell me how to treat differentiation as an operator?

Here is a simple example:

(The content of the worksheet is supposed to be here, but that did not work)


The 'coeff' operation shows 'psi__d0' as the only coefficient of 'Delta__delta(t)', while what I wanted to see is the 'Desired' expression in the worksheet, '(psi__d0 + psi__q0 / omega__0 * D)' as the coefficients. Here, 'D' represents the differentiation. 

Thank you, 

In Kwon Park 

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