Help with non-linear regression, SPSS

[fortenberry]

Hey all
New to the forums and was hoping for some help with writing out part of a non-linear regression model from somebody brighter than me.
So one part of the model contains a Boolean expression and goes something like this
X=TL if T>TM or X=TU if T>TM
So for each iteration, T is supposed to be compared with the estimated TM so that if T<TM is true and T>TM is false then X=TL and vice versa.

Fairly new to SPSS and this might be really simple, but I just don't know how to syntax this into the model, I simply can't write it out correctly, which is very frustrating . I have PASW 18. If any of you could help me it would be most appreciated
Thanks so much for your help

 

[Dason]

X=TL if T>TM or X=TU if T>TM
So for each iteration, T is supposed to be compared with the estimated TM so that if T<TM is true and T>TM is false then X=TL and vice versa.

I don't know anything about SPSS so I can't help you there. However I think you might have something mixed up in the part I quoted. You have the same logical condition giving two separate things in that first line. What exactly do you mean?

 

[fortenberry]

Basically the parameter X is supposed to switch between the two different parameters (Tl and Tu, estimated by the model), depending if the value is above or below TM (the optimum temperature in my case). So if X>TM it takes the value Tu, but if the opposite is true(X<TM), then X = Tl. I miss spelled in my post, sorry, too little coffe or too much.
Thanks