Second order delay differential equation in julia

When working with second order delay differential equations in Julia, there are several approaches you can take to solve them. In this article, we will explore three different methods and compare their effectiveness.

Method 1: Direct Integration

The first method involves directly integrating the delay differential equation. This can be done by converting the second order equation into a system of first order equations using a change of variables. Let’s take a look at the code:


using DifferentialEquations

function f(du, u, p, t)
    du[1] = u[2]
    du[2] = -p[1]*u[2] - p[2]*u[1](t-p[3])
end

u0 = [1.0, 0.0]
p = [1.0, 1.0, 1.0]
tspan = (0.0, 10.0)

prob = DDEProblem(f, u0, p, tspan)
sol = solve(prob)

This method is straightforward and can be easily implemented. However, it may not be the most efficient approach for complex delay differential equations.

Method 2: Discretization

The second method involves discretizing the delay differential equation and solving it using numerical methods. This can be done by dividing the time interval into smaller intervals and approximating the solution at each interval. Here’s an example of how this can be done:


using DifferentialEquations

function f(du, u, p, t)
    du[1] = u[2]
    du[2] = -p[1]*u[2] - p[2]*u[1](t-p[3])
end

u0 = [1.0, 0.0]
p = [1.0, 1.0, 1.0]
tspan = (0.0, 10.0)
dt = 0.01

t = collect(tspan[1]:dt:tspan[2])
u = zeros(length(t), length(u0))

u[1, :] = u0

for i in 2:length(t)
    u[i, :] = u[i-1, :] + dt*f(u[i-1, :], p, t[i-1])
end

This method provides more control over the discretization process and allows for fine-tuning of the numerical solution. However, it can be more computationally expensive and may require additional optimization.

Method 3: Delay Differential Equation Solver

The third method involves using specialized delay differential equation solvers. These solvers are specifically designed to handle delay differential equations efficiently. Here’s an example of how this can be done:


using DifferentialEquations

function f(du, u, h, t)
    du[1] = u[2]
    du[2] = -h[1]*u[2] - h[2]*u[1](t-h[3])
end

u0 = [1.0, 0.0]
h = [1.0, 1.0, 1.0]
tspan = (0.0, 10.0)

prob = DDEProblem(f, u0, h, tspan)
sol = solve(prob)

This method is the most efficient and reliable for solving second order delay differential equations in Julia. It takes advantage of specialized solvers that are optimized for this type of problem.

In conclusion, while all three methods can be used to solve second order delay differential equations in Julia, the third method using a specialized delay differential equation solver is the most efficient and reliable option. It provides accurate results and takes advantage of optimized solvers. However, the choice of method ultimately depends on the specific requirements and complexity of the problem at hand.

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