``derivs_int()''

Write a derivs routine of the following form appropriate for solution of the equation $\frac{dy}{dx}=f(x)$, a simple one-dimensional ODE. Note that because the ODE is one-dimensional, there is only one component, $\frac{dy}{dx}$=dydx[1].

void derivs_int(double x, double y[], double dydx[],
            int k, double f[], double r[], double dr[], int N)

Output:

• dydx[1]: derivative $\frac{dy}{dx}(x)=f(x)$

Input:

• x: point where $\frac{dy}{dx}(x)$ is evaluated.
• y[1]: value of $y(x)$.
• k: array index corresponding to x, so that x=r[k].
• f[]: array of function values so that f(r[k])=f[k].
• r[], dr[], N: information describing change of variables.