i am trying nonlinear for nonlinear ode using by finite difference method

i am trying nonlinear for nonlinear BVP using by finite difference method.

y''+a*e^y=0, y(0)=y(1)=0.

The difference equations:

\frac{y_{i+1}-2y_i+u_{i-1}}{h^2}+a* e^{y_i}=0, i=1,\dots, n-1,

Code:

maxiter=4;
lamb=1;
n=20;

Unrecognized function or variable 'df'.

Answer 1

[Torsten]

You want to solve a nonlinear system of equations using Newton's method, but you didn't supply the Jacobian "df". i.e.

df{i}/dx(j) (i,j = 2,...,n-1).

[Torsten]

Works (see above).