CFD Online Discussion Forums - Add custom function

Hello everyone,

I want to apply a custom equation solver to the source term
y= $x^{3}$ *T+ $x^{2}$ +1
y=-x+100

Then combine the two equations：
$x^{3}$ *T+ $x^{2}$ +1+x-100=0
Solve iteratively to find x, and back-substitute the equation to find y

source item
S=y*100+2.5e5

I want to know how to apply the obtained results to the source terms through iteration.Which macro do I need to call?
I would be grateful if you could provide advice！