TL431: Calculation of r & c for tl431feedback loop in dc dc converter

Hi I was designing a dc dc converter using LM5030 

I was using tl431 and pc817 for designing feedback loop

I know two resistors r5 and r3 are used to set the voltage

but i have seen in many places c1 r2 and r4 are used, they are related to something type 2 compensator

I am a newbie to this and the materials available over the internet are confusing ,can anyone tell why there resistor capacitors are used and how to calculate them