# Simple differential equation question

If I have:
$$\frac{dA(t,z)}{dz}$$

is it possible to convert this to a differential in the form:
$$\frac{dI(t,z)}{dz}$$
given that $$I(t,z)=|A(t,z)|^2/a$$? (Where $$a$$ is a constant).

Any advice would help, thanks.

## Answers and Replies

tiny-tim
Homework Helper
hi n0_3sc!

dI(t,z)/dz would be (2/a) A(t,z).dA(t,z)/dz

so there's no complex conjugate anywhere?

tiny-tim
Homework Helper
now i'm totally confused

are you saying that A is complex, but I is real?

(and in any case, I has two copies of A, and A (obviously) only has one)

Sorry, A is a complex quantity so |A(t,z)|^2=A(t,z)A*(t,z)

I'm confused about differentiating that.

tiny-tim