description of highlighted code

what does it represent n highlighted area

Answer 1

[ScottB]

The first line of the highlighted code means the element of matrix dxdt in row 1 column 1 is equal to the second element of the vector X.

The second line means the element of matrix dxdt in row 2 column 1 is equal to the subsequent expression.

Answer 2

[Steven Lord]

From the variable names and the signature, this looks like a function you wrote or were given as part of solving a system of ODEs. If you're not sure how to use this to solve such a system, see the "Solve Nonstiff ODEs" and "Solve Stiff ODEs" topics on that documentation page; they each walk through an example of how to translate the mathematical form of a system of ODEs into a solution using the ODE solver functions like ode45 or ode15s.