Help Growth Models - Derivates

[acocac]

Hi! I am amateur in mathemathicals growth models but I am doing my graduated work in adjust five differents models in some growth parameters in onion,

[PLAIN]http://img820.imageshack.us/img820/2929/models.png

So my doubt is basically in a derivate for gauss model, i can't derivate this model and it had been adjust for some parameters. So i need to know a derivate for continue my growth analysis.

Also, I just don't know if a sentence of that model is right or wrong, same for others models and their derivates. I read some books about nonlinear models and found diferents expressions in Monomolecular, logistic and Richards models, so i put as options (1 and 2). I also have doubt which are right.

Im grateful with your helps. I'm not physics student, I'm agronomist so you could know better,

Thanks,

 

[HallsofIvy]

If you just go ahead and differentiate the Gauss function, [itex]Y= \alpha e^{-k(t-\gamma)^2} you get <br /> $$\frac{dY}{dt}= -2k\alpha (t- \gamma)e^{-k(t-\gamma)^}$$<br /> which is the same as<br /> $$\frac{dY}{dt}a= -2k(t- \gamma)Y$$<br /> <br /> I see no difference at all between your "options" for the Logistic Equation and only differences in the way the constants are written for the exponential and Richards equations.[/itex]

 

[Mark44]

Fixed the LaTeX for readability.

If you just go ahead and differentiate the Gauss function, $$Y= \alpha e^{-k(t-\gamma)^2}$$ you get
$$\frac{dY}{dt}= -2k\alpha (t- \gamma)e^{-k(t-\gamma)^}$$
which is the same as
$$\frac{dY}{dt}a= -2k(t- \gamma)Y$$

I see no difference at all between your "options" for the Logistic Equation and only differences in the way the constants are written for the exponential and Richards equations.

 

[acocac]

Thanks Mr. Hall,

But i don't know if I am wrong but when you showed a derivate, it should be dY/dt so i don't understand but parameters as gama and t shouldn't be in the derivate as you can see as others models.

I hope you could understand,