Deriving Kirchhoff's equation for this circuit

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Please help me!
I can't understand how to get equation of Kirchhoff to this scheme.
Thank you!

http://i5.pixs.ru/storage/4/3/0/shemaJPG_8094561_3553430.jpg

 

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You have to model the diodes and op-amps and then apply your loop equations. A diode is a voltage-driven current source, something like i=c( exp(a*v)-1 ) where c and a are constants. The op amps are a little trickier, you have to model each terminal as a grounded voltage source.

For this kind of system, it is easier to simulate it by deriving the equations of charge using Lagrangian mechanics approach (because all these elements have mechanical analogies) but this is too long to explain here.