Help with understanding op amp circuit using diodes at the output
The OpAmp is used in an inverting configuration, i.e. when you apply a positive Vi, the output Vo will be negative. So, the current flows through R3 and the upper path (R1, D1), while current through the lower path is blocked by D2.
So, for a positive input, Vo+ will be negative and Vo- will be zero.
The exact value on Vo+ is determined by the ratio of R3 and R1, as the output terminal Vo will be a value which cancels out the voltage at the negative input terminal.

To examine this a bit more, you can do a simulation, even here. I've drawn your circuit using the circuit designer of EE. Click on simulate this circuit and do a DC sweep for Vi.







simulate this circuit &ndash; Schematic created using CircuitLab

The following picture shows the result, blue is Vo+, orange Vo-. I've also added Vo (brown) just to see the effect of the diodes. (Click the image to enlarge)