# How To Solve Systems Of Differential Equations Using Numerical Analysis Techniques

April 21, 2023 Melina Ryber
Australia
Numerical Analysis
Melina is a highly qualified expert who has been helping students with their numerical analysis assignments for more than five years. She boasts a Bachelor’s degree in Mathematics from Adelaide University. You can trust her with your assignment.

Many different phenomena are modeled using differential equations in a variety of disciplines, including physics, engineering, biology, economics, etc. Analytical differential equation solving can be fairly difficult, and there are frequently no exact solutions. Numerical techniques are employed in these situations to resolve the differential equations.

The goal of numerical methods is to approximate the solution of a differential equation. One such technique is solving systems of differential equations with numerical analysis. We will talk about numerical analysis in this blog post to solve differential equation systems.

## What Exactly Are Differential Equation Systems?

A collection of two or more differential equations that are connected is referred to as a system of differential equations. These equations can be expressed as a matrix using the formula: dY/dt = AY.

where t is the independent variable, t is a vector of functions, and A is a matrix of coefficients. The vector function Y(t), which provides the answers to all of the differential equations in the system, is the solution to this system of differential equations.

## Numerical Analysis Techniques Used To Solve Differential Equations Systems

There are numerous numerical techniques available to solve differential equation systems. The Euler method and the Runge-Kutta method, two frequently used numerical techniques, will be covered in this blog.

1. Euler Method:
2. A first-order method for resolving differential equation systems is the Euler method. It entails using the values from the previous time step to approximate the solution at each subsequent time step. The fundamental principle of the Euler method is to forecast the value of the function at the following time step using the derivative at the current time step.

The following formula forms the foundation of the Euler method:

Where h is the step size, f(Y(t)) is the derivative of Y(t), and Y(t) is the solution at time t, Y(t + h) = Y(t) + h * f(Y(t)).

The aforementioned formula must be changed as follows to apply the Euler method to a system of differential equations:

Y(t + h) is equal to Y(t) + h * f(Y(t), t), where f(Y(t), t) is a vector of Y(t)'s derivatives concerning time t.

### Understanding The Euler Method

A straightforward and popular numerical approach for resolving ordinary differential equations is the Euler method. It is a first-order approach that uses a forward difference approximation for the derivative to estimate the differential equation's solution. In comparison to other numerical approaches, the method is simple to use and computationally less expensive, but it may not be very precise, especially for large step sizes.

### How To Apply The Euler Method

We need to take a few actions to solve a first-order ordinary differential equation using the Euler method. The dependent variable's initial value and the associated independent variable must be specified first. The distance between the sites at which we wish to compute the approximate answer is the next thing we must decide. Finally, we can compute the approximate values of the dependent variable at the chosen positions using the Euler method formula.

### Modifications To The Euler Method

The Euler technique has undergone several enhancements to solve its flaws and boost precision. The modified Euler method, which determines the value of the solution at the end of each time step by averaging the slopes at the start and end of each time step, is an example of such an improvement. Heun's method is another advancement that uses a predictor-corrector strategy to increase the solution's accuracy. The Euler technique is now more adaptable and precise for solving ODEs because of these and other advancements.

Although the Euler method is easy to use, it is not extremely precise. The step size h determines how much inaccuracy is introduced into the Euler technique. Therefore, we must reduce the step size to increase accuracy.

3. Runge-Kutta Method:
4. A higher-order method for resolving differential equation systems is the Runge-Kutta approach. To approximate the solution, numerous intermediate values must be calculated at each time step. The fundamental principle of the Runge-Kutta method is to calculate the value of the function at the subsequent time step using a weighted average of the intermediate values.

The most popular method for solving differential equation systems is the fourth-order Runge-Kutta method.

The following formula serves as the foundation for the fourth-order Runge-Kutta method:

Y(t + h) = Y(t) + (1/6) * The intermediate values are (k1 + 2k2 + 2k3 + k4), where h is the step size, and k1, k2, k3, and k4 are determined using the following formulas.

h * f(Y(t), t), k1 = k2 = h * f(Y(t) + (1/2) * k1, t + (1/2) * h) k3 = h * f(Y(t) + (1/2) * k2, t + (1/2) * h) k4 = h * f(Y(t) + k3, t + h), where the vector of Y(t) derivatives is represented by f(Y(t), t).

### Understanding The Runge-Kutta Method

The Runge-Kutta method is a numerical approach for resolving sets of ordinary differential equations. It is predicated on the notion of approximating the solution at the following time step using a weighted average of many slopes. To achieve an approximation of the solution, the procedure entails evaluating the function at several locations within a time step and aggregating the results.

### Procedure For The Runge-Kutta Method

A weighted average of four estimations is used to calculate the answer at each time step of the iterative Runge-Kutta method. The derivatives of the solution are assessed at various times during the time step to derive these estimates. The most widely used variant of the Runge-Kutta algorithm generates four estimates of the solution at each time step. This is known as the fourth-order Runge-Kutta technique.

The fourth-order Runge-Kutta method can be divided into the subsequent steps:

1. Determine the derivative of the solution at the beginning of the time interval.
2. Estimate the answer at the halfway point of the time step using this derivative.
3. Determine the solution's derivative at the halfway point of the time step.
4. Estimate the answer at the halfway point of the time step using this derivative.
5. Determine the solution's derivative at the halfway point of the time step.
6. Estimate the solution after the time step using this derivative.
7. At the conclusion of the time step, compute the derivative of the answer.
8. To get the precise solution after the time step, use a weighted average of the four guesses.

The estimates made at the midway of the time step, which are more accurate than the estimates calculated at the beginning and end of the time step, are given more weight by the weighted average utilized in the fourth-order Runge-Kutta technique.

Since it gathers more data to estimate the solution at each time step, the fourth-order Runge-Kutta approach is more precise than the Euler method. In some cases, the approach is superior to the Euler method since it can accommodate bigger step sizes. In contrast to the Euler technique, the Runge-Kutta method is computationally more expensive and calls for more calculations every time step.

In conclusion, the Runge-Kutta method is a powerful numerical technique for resolving differential equation systems. Compared to the Euler method, it allows for more accurate solutions due to its iterative nature and use of weighted averages. The cost and complexity of calculation have increased as a result, though.

## The Benefits And Drawbacks Of The Euler And Runge-Kutta Methods

Comparing the Euler technique to the Runge-Kutta method, the Euler approach is simpler to use and less expensive to compute. However, the Euler approach might result in major mistakes in the solution because it is not particularly accurate, especially for large step sizes.

On the other hand, the Runge-Kutta method can accommodate bigger step sizes and is more accurate than the Euler approach. In contrast to the Euler technique, it is computationally more expensive and necessitates more calculations per time step.

The particular problem that needs to be solved determines which numerical approach should be used. The Runge-Kutta method is better suited for problems requiring great accuracy, although the Euler approach can be employed if the computational economy is more crucial.

## Application Of Numerical Methods For Solving Systems Of Differential Equations

There are many different disciplines in which numerical methods for solving differential equation systems are applied. In this section, we will go over a few instances when systems of differential equations can be solved numerically.

### Lotka-Volterra Equations:

The predator-prey interaction in an ecosystem is modeled using the Lotka-Volterra equations, a pair of differential equations. The equations are as follows: dX/dt = X - XY; dY/dt = XY - Y; where X, Y, and are constants and X, Y, and are populations of prey and predator, respectively.

We may first rewrite the differential equations in matrix form as dY/dt = AY,

where A = [ α -β ] [ δ -γ ]

Either the Euler or Runge-Kutta method can be used to find the solution to this system of differential equations.

### Equations For Electrical Circuits:

A set of differential equations can be used to simulate the behavior of electrical circuits.

The differential equations for this circuit are provided as follows: dVc/dt = -1/(R1C1) * Vc + 1/(R1C1) * Vs dVs/dt = -1/(R2C2) * Vs + 1/(R2C2) * Vc where R1, R2, C1, and C2 are constants and Vc is the voltage across the capacitor and Vs is the voltage across the voltage source.

We can first rewrite the differential equations in matrix form as: dY/dt = AY + B where Y = [Vc, Vs] to solve this system of differential equations numerically.

A = [-1/(R1C1) 1/(R1C1)] [ 1/(R2C2) -1/(R2C2) ]

B = [0, 1/(R2C2) * Vs]

Either the Euler or Runge-Kutta method can be used to find the solution to this system of differential equations.

## Conclusion

The use of numerical methods to solve differential equation systems is widespread in many different disciplines. The Euler method and the Runge-Kutta method for resolving differential equation systems were covered in this blog. We also covered their benefits and drawbacks and gave illustrations of how these techniques could be used to address problems in the real world. To ensure accuracy and computational effectiveness, it is crucial to select the proper numerical approach based on the particular problem being tackled.