@Preben Alsholm 

Haha, thanks man, you're amazing !!

indeed it comes from engineering.

E refers to the Young's modulus, I is the moment of inertia.

It's the equation that gives the displacement of a portion of a building  along the X axis ( which depends on y and t : altitude and time ) .

@Preben Alsholm 

Hi thank you for your help ! It's a nice graph.

But how do i choose initial functions ?