Variable not found

New to Julia
1

Hi Guys

Please refer to the below code. It was running perfectly and now for some reason I am getting the following error, “ERROR: UndefVarError: sol not defined”. Which makes no sense it has been defined…

Any assistance would be appreciated.

using Plots
using DifferentialEquations

function sdof!(dx,x,p,t)
    m,k,c,f,w = p
    dx[1] = x[2]
    dx[2] = (-c*x[2]-k*x[1]+f*sin(w*t))/m
end


nf = [9.69,57.77,127.28,174.53,313.719]*6.28 # [rad/s]
m =  [74.11,13.241,2.4,3.4,2.366]/100# [%]

f = 1000 # [N] forcing function
M = 611.778



tspan = (0,1)
x0 = [0.00,0.00]
T_displacement = zeros(length(tspan[1]:0.001:tspan[2]))

for i in 1:length(nf)
    k = nf[i]^2*m[i]*M
    c = 0.01*(m[i]*M+k)
    p = m[i]*M,k,c,f,50*6.28
    prob = ODEProblem(sdof!, x0, tspan, p)
    sol = solve(prob, Tsit5(), reltol=1e-8, abstol=1e-8, saveat = 0.001)
    T_displacement += sol[1,:]
end

plotly()

#plt_1 = plot()
display(plot(sol.t,T_displacement,xlabel = "Time (sec)", ylabel = "Displacement (m)"))
2

sol is a local variable and is not defined in the global scope, see Scope of Variables · The Julia Language

Use global sol = solve(...).

3

If you define a variable inside a loop, it’s not available outside the loop:

julia> for i in 1:10
           x = 1
       end

julia> x
ERROR: UndefVarError: `x` not defined

The solution is to add global:

julia> for i in 1:10
           global x = 1
       end

julia> x
1

It’s better style to put code into functions - it’ll run faster, and be more debuggable. If you do anything bigger than a throwaway script, or to quickly test something, I recommend doing that.

1 Like
4

Hi Guys

Thanks for the replies, I just figured out the issue a few minutes after posting.