Converting 0-5 volts (linear) to +2.5 -- 0 -- +2.5 volts ("vee")
Here is one way to do it that uses a cheap quad op amp and a bunch of 100K resistors (and operate from a single +5V supply): 







simulate this circuit &ndash; Schematic created using CircuitLab

OA1 provides the two reference voltages used from the supply. 

OA2 subtracts the input voltage from 2*1.25V to give the left part of the output.

OA3 subtracts 2.5V from the input voltage for the right part of the output
(both saturate at 0V with a single 5V supply, so no diodes are required).

OA4 sums the two to give the desired output voltage.