10.1.6 - Worked-Out Example
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Introduction to Modified Euler's Method
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Today, we're exploring the Modified Euler’s Method, which helps us find numerical solutions to differential equations more accurately. Can anyone tell me why we can't always use exact analytical solutions?
Sometimes the differential equations are too complex to solve analytically!
Exactly! That's why we have numerical methods. The Modified Euler's Method improves the accuracy of the basic Euler's method by averaging slopes. Does anyone remember how the basic Euler's method works?
It's about using the slope at the start of the interval to predict the next point.
That's right! Now, Modified Euler's adjusts this prediction by considering the slope at both the beginning and the end. Think of it as checking where you're going halfway through the journey. Ready to dive into an example?
Worked-Out Example Setup
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Let's set up our first example. We have the equation \( \frac{dy}{dx} = x + y \) with initial condition \( y(0) = 1 \). What step size do we have?
We have a step size of 0.1!
Correct! Now, can anyone tell me the initial values we will be using?
So, \( x_0 = 0 \) and \( y_0 = 1 \)?
Yes! Now we are ready to take our first step using the Modified Euler's Method!
First Iteration Breakdown
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Let's begin our first iteration. We first need to calculate \( k_1 \). Who can tell me what \( k_1 \) is?
It's \( f(x_0, y_0) \), which is \( 0 + 1 = 1 \)!
Great! So, what’s our predicted \( y^* \)?
\( y^* = 1 + 0.1 \cdot 1 = 1.1 \)!
Perfect! Now how do we calculate \( k_2 \)?
It's \( f(0.1, 1.1) \), which gives us \( 0.1 + 1.1 = 1.2 \)!
Well done! Finally, how do we get the corrected value \( y_1 \)?
\( y_1 = 1 + \frac{0.1}{2} (1 + 1.2) = 1.11! \)
Second Iteration Analysis
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Moving on to the second iteration! What are our new values for \( x \) and \( y \)?
\( x_1 = 0.1 \) and \( y_1 = 1.11 \).
Yes! Now, what is \( k_1 \) for this step?
It will be \( f(0.1, 1.11) = 0.1 + 1.11 = 1.21 \)!
Wonderful! Now let's predict \( y^* \). What do we have?
\( y^* = 1.11 + 0.1 \cdot 1.21 = 1.231 \)!
Great job! Finally, let’s compute \( k_2 \) and our corrected value!
For \( k_2 \), we find \( f(0.2, 1.231) = 1.431 \), and the corrected \( y_2 \) is about \( 1.24205 \)!
Conclusion and Summary
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To summarize, how did we find our final value using the Modified Euler’s Method?
We iterated twice, using the slopes to predict and then correct our values.
We ended with \( y(0.2) \approx 1.24205 \)!
Exactly! The Modified Euler's method provides a much better approximation than standard Euler’s method by taking the average of slopes. Any final questions?
How does this compare to higher order methods like Runge-Kutta?
Great question! While Modified Euler's is simple and quite effective, methods like Runge-Kutta offer even greater accuracy, though at the cost of more function evaluations.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, the application of the Modified Euler’s Method is demonstrated through a step-by-step worked-out example. The example illustrates how to predict and correct the value of a differential equation at a specific point, emphasizing the method's improved accuracy over standard Euler's method.
Detailed
Worked-Out Example
Introduction
This section presents a detailed example of using the Modified Euler's Method (also known as Heun's Method or the Improved Euler Method) to find an approximate solution of the initial value problem (IVP) defined by the differential equation
$$ \frac{dy}{dx} = x + y, \quad y(0) = 1, \quad h = 0.1. $$
Step-by-Step Solution
- Initial Values: The initial values are set as follows:
- $$x_0 = 0$$
- $$y_0 = 1$$
- $$h = 0.1$$
- First Iteration:
- Compute the initial slope:
$$k_1 = f(x_0, y_0) = 0 + 1 = 1$$ - Predict the next value:
$$y^* = y_0 + h \cdot k_1 = 1 + 0.1 \cdot 1 = 1.1$$ - Compute the corrected slope:
$$k_2 = f(0.1, 1.1) = 0.1 + 1.1 = 1.2$$ -
Calculate the corrected value:
$$y_1 = y_0 + \frac{h}{2} (k_1 + k_2) = 1 + 0.05(1 + 1.2) = 1.11$$ - Second Iteration:
- Update the values:
- $$x_1 = 0.1, y_1 = 1.11$$
- Compute the new slope:
$$k_1 = f(0.1, 1.11) = 0.1 + 1.11 = 1.21$$ - Predict the next value:
$$y^* = 1.11 + 0.1 \cdot 1.21 = 1.231$$ - Correct the slope:
$$k_2 = f(0.2, 1.231) = 0.2 + 1.231 = 1.431$$ - Calculate the corrected value:
$$y_2 = 1.11 + \frac{h}{2} (k_1 + k_2) = 1.11 + 0.05(1.21 + 1.431) = 1.24205$$
Conclusion
The final approximation is
$$ y(0.2) \approx 1.24205 $$, illustrating the Modified Euler's Method as a more accurate alternative to the basic Euler Method.
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Initial Values Setup
Chapter 1 of 4
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Chapter Content
- Step 1: Initial values
- 𝑥 = 0, 𝑦 = 1, ℎ = 0.1
Detailed Explanation
In this step, we establish the initial values needed for the Modified Euler's Method. Here, we set the initial value of 𝑥 to 0 and the initial value of 𝑦 to 1. The step size ℎ is set to 0.1, indicating that we will compute the function's value in increments of 0.1 from the starting point.
Examples & Analogies
Imagine you're planning a short road trip. You start your journey at mile marker 0 (your starting point), and you know you'll be traveling 0.1 miles at a time. The initial mile marker (𝑥) is 0, and your car’s initial mileage (𝑦) is 1 mile. You are ready to start this trip.
First Iteration Calculation
Chapter 2 of 4
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Chapter Content
- Step 2: First Iteration
- 𝑘 = 𝑓(𝑥 ,𝑦 ) = 0 +1 = 1
- Predictor:
𝑦∗ = 𝑦 +ℎ ⋅𝑘 = 1+ 0.1⋅1 = 1.1 - 𝑘 = 𝑓(𝑥 ,𝑦∗) = 𝑓(0.1,1.1) = 0.1 +1.1 = 1.2
- Corrected value:
ℎ𝑦 = 𝑦 + (𝑘 + 𝑘 ) = 1 + (1+ 1.2) = 1+ 0.1⋅1.1 = 1.11
Detailed Explanation
In the first iteration, we calculate the value of 𝑘 by substituting the initial values into the function 𝑓. Here, 𝑖𝑓(𝑥 ,𝑦 ) gives us 1. Next, we predict the next value 𝑦∗ using the formula provided, resulting in 1.1. We then compute another 𝑘 using the predicted value 𝑦∗ before determining the corrected value of 𝑦, which gives us approximately 1.11 at the end of the first step.
Examples & Analogies
Continuing with our road trip, after traveling from the starting point, you assess how far you've come based on the current mileage and then predict how far you will be after the next increment. You also refine your estimate by recalculating based on your new position along the route, arriving at a slightly adjusted distance from the start.
Second Iteration Calculation
Chapter 3 of 4
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Chapter Content
- Step 3: Second Iteration
- 𝑥 = 0.1, 𝑦 = 1.11
- 𝑘 = 𝑓(0.1,1.11) = 0.1 +1.11 = 1.21
- Predictor:
𝑦∗ = 1.11+ 0.1⋅1.21 = 1.231 - 𝑘 = 𝑓(0.2,1.231) = 0.2 +1.231 = 1.431
- Corrected value:
𝑦 = 1.11+ (1.21 +1.431) = 1.11 +0.1 ⋅1.3205 = 1.24205
Detailed Explanation
In the second iteration, we use the updated values of 𝑥 and 𝑦 from the first iteration. We calculate 𝑘 again, yielding a value of 1.21. Using this, we predict 𝑦∗ to be 1.231. After computing a new 𝑘 for 𝑦∗, we find the corrected value of 𝑦 to be approximately 1.24205, after averaging the slopes and adjusting our original estimate.
Examples & Analogies
On your road trip, after traveling a short distance, you double-check your route to see if you're on track. You re-evaluate your speed for the next leg of your journey and adjust your expected arrival marker based on this newly acquired info, resulting in a slightly adjusted mileage that reflects your real-time position.
Final Result
Chapter 4 of 4
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Chapter Content
- Final Answer:
- 𝑦(0.2) ≈ 1.24205
Detailed Explanation
At this point, we have completed the calculations required by the Modified Euler's Method. The approximated value of 𝑦 at 𝑥 = 0.2 is around 1.24205. This gives us a better understanding of how the solution behaves after applying the numerical method over the specified interval.
Examples & Analogies
After your road trip, you take a moment to reflect on the journey. You've successfully navigated to your destination, realizing how much more accurate your estimates were thanks to your careful recalculations along the way. Just like how you reach an accurate mark on your journey, we arrive at a close approximation of y using the Modified Euler's Method.
Key Concepts
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Modified Euler’s Method: A second-order numerical technique that improves the accuracy of Euler's method by averaging slopes.
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Initial Value Problem: A problem where the initial condition of a function is known, and the goal is to find its values at subsequent points.
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Slope Calculation: Key in both the prediction and correction steps of the Modified Euler’s Method.
Examples & Applications
Using Modified Euler's Method on the equation \( \frac{dy}{dx} = x + y \) with \( y(0) = 1 \) gives a sequence of approximations leading to \( y(0.2) \approx 1.24205 \).
An initial value problem for a first-order ODE for a different equation can also be approached similarly using the same method.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
To find that y, don't just guess, use k's and h, it's for the best!
Stories
Once upon a time, two slopes met on a hill, one said follow me, the other to stand still. Together they took a step down, and found a better point around.
Memory Tools
Use Kappa to Stay True with Modified Euler: K1, predict, K2, average!
Acronyms
M.E.M. - Modified Euler's Method means More Effective Model!
Flash Cards
Glossary
- Modified Euler’s Method
A numerical method to solve initial value problems more accurately than the standard Euler's method by using the average of the slopes at the start and end of the interval.
- Firstorder ODE
An ordinary differential equation involving the first derivative of a function.
- Initial Value Problem (IVP)
A type of problem where the solution of the differential equation is determined by the value of the function at a specific point.
- Slope
The rate of change of a function, often represented as the derivative.
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