OpAmp with negative feedback used to build a variable voltage source with linear control around +- zero volts.
Formula: v_out = 2 v_+ - v_in
with v_+ is the constant voltage at noninverting input of the OpAmp.
Example: With a constant v_+ = 2.5V a variable input voltage v_in in the range of 0 … 10V leads to an output voltage v_out in the range of 5 … -5V.
This calculation is independent of the resistor values R1 and R2 (except of the current flow in the circuit) and also independent of an inverting or non-inverting OpAmp configuration that is used.
Ref. GOL
