# One-dimensional NLS using MethodOfLines 'type Array has no field lhs`

I’m trying to solve the one-dimensional nonlinear Schrodinger equation using MethodOfLines. I looked at the code on the docs: http://methodoflines.sciml.ai/dev/tutorials/brusselator/, and adapted it as:

``````using ModelingToolkit, MethodOfLines, OrdinaryDiffEq, DomainSets

@parameters x z
@variables A(..)
Dx   = Differential(x)
Dz   = Differential(z)
Dzz  = Differential(z)^2

xmin = 0.
xmax = 1e-1
zmax = 10.
zmin = -zmax

c0 = 1.
A0(x,z) = c0*sech(c0*z/sqrt(2))*exp(im*c0^2*x/2)

domains = [x ∈ Interval(xmin,xmax), z ∈ Interval(zmin,zmax)]

eq = [im*Dx(A(x,z))+Dzz(A(x,z)) ~ -abs2(A(x,z))*A(x,z)]
bcs = [A(xmin,z) ~ A0(xmin,z),
A(x,zmin) ~ 0,
A(x,zmax) ~ 0]

@named pdesys = PDESystem(eq,bcs,domains,[x,z],[A(x,z)])

N       = 100
dz      = 1/N
order   = 2

discretization = MOLFiniteDifference([z=>dz], x)

@time prob = discretize(pdesys,discretization)
``````

However this won’t run, giving error `type Array has no field lhs`. I think the only main difference between my code and the tutorial is that my PDE is for a single function, but I don’t know why that would be causing this error.

Does anyone have any ideas why?

Open an issue. Might just be a missing tag.

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