V3 will be a fixed voltage V4 will be output of differential amplifier
what im trying to do is dual supply that goes 0-15 volts and 10mA-1A this is positive part of the supply, lm337 will provide -1.25v for the lm317 to go to 0 volts, transistor is supposed to short adj pin to -1.25 resulting in 0 volts at the output i used mosfet because with bjt i didnt get 0 volts at the output only 0.6 when i did simulation , opamp is used as comparator which will turn on and off transistor, comparator will have ref voltage and the voltage coming out from the differential amplifier which is not in schematic its what v3 and v4 are for.