Suppose b(x) is a function of a variable x, and let Dxx represent the second derivative d^2x/dx^2. Then the differential equation

1+Dxx u = b

has solution

u = (1+Dxx)\b.

I can’t figure out how to do this with `DiffEqOperators.jl`

.

Let’s first consider the simpler equation: Dxx u = b. This can be solved as:

```
using DiffEqOperators
L = 2*pi
nx = 100
dx = L/(nx+1)
xpoints = range(dx, step=dx, length=nx)
b = sin.(xpoints)
Dxx = CenteredDifference(2, 2, dx, nx)
bc = Dirichlet0BC(Float64)
sol = (Dxx*bc)\b
```

Based on this I want to do something like `(1+Dzz*bc)\b`

. However I can’t see how to make this work. I’ve tried using `I`

from the `LinearAlgebra`

package, the identity matrix, and a `CenteredDifference`

of order zero, but all gave an error. Does anyone know what the solution is?