Sine function approximation circuit. How does this work?
Might be a Sine Generator if the resistor Network is calculated in a way so an digital input angle from 0-90° is resulting in correct steps of a sine. guess with Ei you can supply either 0 or 1 to select sine or cosine.
I am to lazy to recalculate the circuit, but the formulas must be the amplification defined by R1, R2 as these are constant and A is a constant.

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Without going into details, this looks like a digital to analog converter to me. You may produce a sine if the digital signal provides resembles a sine - or whatever form you want.
Sine signals can be generated digitally with cordec or bkm algorithms.
a analog circuit to generate some form of sine needs oscillation at least plus signal shaping is also needed, so one or more energy storage like capacitance or inductance must be present. So this is definitely not a sine (any signal) generator. Signal must be provided digitally