i want the functional form or some idea of the function phi mentioned in the image given below

here phi[a] shows that phi is a function of 'a'. How can I get the functional form of this phi[a] and if it is not possible than can i just have the idea of the functional form of phi ?

[Jan]

All we know about Phi, is that it is a function of a. I do not see a chance to guess, what the correct functional form is.

[John D'Errico]

phi(a) has no "functional" form, something you can derive from that relation. Why not?

While the relation shows phi(a), you can write anything you want. That does not mean you can derive something meaningful from what you wrote. Not only that, all we see is information about the derivative of phi(a).

Anyway, what is shown there is not an equality in any way, but a limit based on an inequality. If I told you that my age is at least 10 years old, would you then be able to infer my correct age?

Finally, there is no question in this about MATLAB, so the question is not even on-topic on this forum.