Getting undefined error for function

You define a function etaB, but try to evaluate a function etaT which is nowhere defined?

Furthermore your range variables i and j don't make much sense in the function definition. What did you expect them to achieve?

Defining lambda:=5 is useless because lambda is the (formal) function argument. The value for lambda has to be provided as argument when you call your function.

Did you look for something like this: