18.3 - Example Problems
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Introduction to Volterra Integral Equations
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Today, we’ll delve into Volterra Integral Equations, which can be tricky to handle directly. A Volterra Integral Equation of the Second Kind has the form \( f(t) = g(t) + \int_{0}^{t} K(t - \tau)f(\tau) d\tau \). Can anyone tell me what this equation represents?
Is \( f(t) \) the function we’re trying to solve for?
Exactly! And \( K(t-\tau) \) is known as the kernel. It captures the effect of the past values of \( f(\tau) \). Remember the kernel helps understand how the function behaves over time. Let’s move to how Laplace transforms help us simplify these equations.
Why are Laplace Transforms useful for these equations?
Great question! By transforming the integral equation into algebraic equations using the Convolution Theorem, we significantly simplify the problem. This allows us to manipulate and solve them more easily.
Applying Laplace Transforms
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Let’s apply the Laplace Transform to a Volterra Integral Equation. Here’s the first problem we will tackle: \( f(t) = t + \int_{0}^{t} (t - \tau)f(\tau) d\tau \). What’s our first step?
We begin by applying the Laplace Transform to both sides, right?
Exactly. Applying the transform results in \( F(s) = \frac{1}{s^2} + F(s) \cdot \frac{1}{s^2} \). What's next?
Now we solve for \( F(s) \).
Correct! We isolate \( F(s) \): \( F(s)(1 - \frac{1}{s^2}) = \frac{1}{s^2} \), and simplify it to get \( F(s) = \frac{1}{s^2 - 1} \). Who can remind me what the final step is?
We take the inverse Laplace Transform to find \( f(t) \)!
Precisely! Thus, we find \( f(t) = sinh(t) \). Can you see how efficiently we’ve arrived at the final function?
Example Problem Review
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Now, let’s solve another problem: \( f(t) = e^t + \int_{0}^{t} f(\tau) d\tau \). What’s the first thing we do?
We apply the Laplace Transform to both sides.
Indeed! This gives us \( F(s) = \frac{1}{s - 1} + F(s) \). What do we have next?
We can move \( F(s) \) to the other side and solve it!
Right! We arrive at \( F(s)(1 - \frac{1}{s}) = \frac{1}{s} \), leading us to simplify it to \( F(s) = \frac{s}{(s - 1)(s - 1)} \). What do we do at this stage?
Take the inverse Laplace Transform to find \( f(t) = te^t \).
Perfect! Now we see how the method works. Remember that the Inverse Laplace transform helps find our time domain function efficiently.
Overview of Kernels
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Before we wrap up, let’s review the common types of kernels. Can anyone tell me what types we've encountered?
We have constant, linear, exponential, and sine kernels.
Exactly! Kernel types influence how we apply Laplace transforms. For example, the constant kernel simplifies our work as seen in our earlier problems. Remember the form: \( K(t) = 1 \) corresponds to a more straightforward Laplace Transform. Can everyone recall their respective transforms?
For a constant kernel, it's \( \frac{1}{s} \).
Correct! This information allows us to navigate solving Volterra integral equations using Laplace transforms much more easily.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, we explore key examples that illustrate the use of Laplace Transforms to solve Volterra integral equations. Two specific problems are presented, each with detailed solutions that highlight the steps involved in applying the Laplace Transform and utilizing the Convolution Theorem for successful resolution.
Detailed
Example Problems
This section illustrates the application of Laplace Transforms in solving Volterra integral equations through two detailed examples with supporting solutions.
Key Concepts
Integral equations, such as Volterra Integral Equations of the Second Kind, are often complex to solve directly. However, the application of Laplace Transforms simplifies this process significantly. The importance of the Convolution Theorem allows the transformation of convolutions into algebraic forms, making solving these equations more straightforward.
Example Problem 1 \( f(t) = t + \int_{0}^{t} (t - \tau) f(\tau) d\tau \)
- Step 1: Apply the Laplace Transform.
- Setting both sides to get \( F(s) = \frac{1}{s^2} + F(s)\cdot \frac{1}{s^2} \)
- Step 2: Solve for \( F(s) \) to yield \( F(s)(1 - \frac{1}{s^2}) = \frac{1}{s^2} \), hence \( F(s) = \frac{1}{s^2 - 1} \)
- Step 3: Finally, find \( f(t) \) using the inverse Laplace Transform, resulting in \( f(t) = sinh(t) \).
Example Problem 2 \( f(t) = e^t + \int_{0}^{t} f(\tau) d\tau \)
- Step 1: Apply the Laplace Transform.
- Resulting in \( F(s) = \frac{1}{s - 1} + F(s) \)
- Step 2: Solve which leads to \( F(s)(1 - \frac{1}{s}) = \frac{1}{s} \) leading to \( F(s) = \frac{s}{(s - 1)(s - 1)} \)
- Step 3: Use inverse Laplace Transform to find \( f(t) = t e^t \).
These examples showcase how the approach of using Laplace Transforms and the Convolution Theorem streamlines solving Volterra-type integral equations.
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Example 1: Solving the Integral Equation
Chapter 1 of 2
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Chapter Content
Example 1:
Solve the integral equation:
\[ f(t) = t + \int_0^t (t-\tau) f(\tau) d\tau \]
Solution:
Step 1: Apply Laplace Transform:
\[ \mathcal{L}\{f(t)\} = \mathcal{L}\{t\} + \mathcal{L}\{\int_0^t (t-\tau) f(\tau) d\tau\} \]
\[ F(s) = \frac{1}{s^2} + F(s) \cdot \frac{1}{s^2} \]
Step 2: Solve algebraically:
\[ F(s)(1 - \frac{1}{s^2}) = \frac{1}{s^2} \Rightarrow F(s) = \frac{1}{s^2 - 1} \]
Step 3: Inverse Laplace Transform:
\[ f(t) = \mathcal{L}^{-1}\{\frac{1}{s^2 - 1}\} = \sinh(t) \]
Detailed Explanation
In this example, we are tasked with solving a Volterra integral equation. The first step involves applying the Laplace Transform to both sides of the equation. This converts the time-domain integral into a more manageable algebraic form in the s-domain. Then, we manipulate the resulting equation algebraically to isolate F(s), which represents the Laplace-transform of our unknown function f(t). Finally, we perform the inverse Laplace Transform to retrieve f(t) in the time domain, yielding the final solution as sinh(t).
Examples & Analogies
Imagine trying to solve a mystery where the clues are scattered everywhere (the integral equation). The Laplace Transform acts like a detective's magnifying glass, helping you see the clues clearly and gather them together into a coherent picture (the algebraic form). Solving the equation is like piecing together the mystery, and the inverse Laplace Transform gives you the final picture of what happened.
Example 2: Another Integral Equation
Chapter 2 of 2
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Chapter Content
Example 2:
Solve:
\[ f(t) = e^t + \int_0^t f(\tau) d\tau \]
Solution:
Apply Laplace Transform:
\[ F(s) = \frac{1}{s-1} + F(s) \cdot \frac{1}{s} \Rightarrow F(s)(1 - \frac{1}{s}) = \frac{1}{s-1} \Rightarrow F(s) = \frac{s}{(s-1)(s-1)} = \frac{s}{(s-1)^2} \]
Now,
\[ f(t) = \mathcal{L}^{-1}\{\frac{s}{(s-1)^2}\} = t e^t \]
Detailed Explanation
In this second example, we're solving a slightly different integral equation. We start by applying the Laplace Transform, which helps us convert the time-domain integral into an algebraic form. After applying the transforms, we manipulate the equation to solve for F(s). The term \( F(s)(1 - \frac{1}{s}) \) reveals a relationship between F(s) and the known function. Once we isolate F(s), we take the inverse Laplace Transform to find f(t), resulting in the function t e^t. This showcases how we can handle differing types of integral equations similarly using Laplace Transforms.
Examples & Analogies
Think of this process like gardening. The integral equation is like starting a garden filled with plants that represent different functions. Applying the Laplace Transform is akin to rearranging the garden layout, making it easier to see how each plant interacts with one another (the algebraic manipulation). Finally, the inverse Laplace Transform is like picking the ripe fruits (finding the solution) ready for harvest.
Key Concepts
-
Integral equations, such as Volterra Integral Equations of the Second Kind, are often complex to solve directly. However, the application of Laplace Transforms simplifies this process significantly. The importance of the Convolution Theorem allows the transformation of convolutions into algebraic forms, making solving these equations more straightforward.
-
Example Problem 1 \( f(t) = t + \int_{0}^{t} (t - \tau) f(\tau) d\tau \)
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Step 1: Apply the Laplace Transform.
-
Setting both sides to get \( F(s) = \frac{1}{s^2} + F(s)\cdot \frac{1}{s^2} \)
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Step 2: Solve for \( F(s) \) to yield \( F(s)(1 - \frac{1}{s^2}) = \frac{1}{s^2} \), hence \( F(s) = \frac{1}{s^2 - 1} \)
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Step 3: Finally, find \( f(t) \) using the inverse Laplace Transform, resulting in \( f(t) = sinh(t) \).
-
Example Problem 2 \( f(t) = e^t + \int_{0}^{t} f(\tau) d\tau \)
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Step 1: Apply the Laplace Transform.
-
Resulting in \( F(s) = \frac{1}{s - 1} + F(s) \)
-
Step 2: Solve which leads to \( F(s)(1 - \frac{1}{s}) = \frac{1}{s} \) leading to \( F(s) = \frac{s}{(s - 1)(s - 1)} \)
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Step 3: Use inverse Laplace Transform to find \( f(t) = t e^t \).
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These examples showcase how the approach of using Laplace Transforms and the Convolution Theorem streamlines solving Volterra-type integral equations.
Examples & Applications
Example 1: Solve \( f(t) = t + \int_{0}^{t} (t - \tau)f(\tau) d\tau \) yielding \( f(t) = sinh(t) \).
Example 2: Solve \( f(t) = e^t + \int_{0}^{t}f(\tau) d\tau \) giving \( f(t) = te^t \).
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
For Volterra, part of the sum, the unknown's under the integral drum.
Stories
Imagine a radio that picks up past signals (the kernel) to play a song (the function) perfectly at a given time!
Memory Tools
Use the acronym 'VLK' for Volterra Kernel Law - where V is for Volterra equations, L for Laplace, and K for kernel.
Acronyms
Remember CALM
Convolution And Laplace Method - a reminder for the approach using Laplace Transforms.
Flash Cards
Glossary
- Integral Equation
An equation in which an unknown function appears under an integral sign.
- Volterra Integral Equation of the Second Kind
A specific type of integral equation that includes the function under the integral sign.
- Kernel
The function \( K(t - \tau) \) in the integral equation affecting the solution's behavior.
- Laplace Transform
A technique for transforming a function of time into a function of a complex variable.
- Convolution Theorem
A theorem stating that the Laplace Transform of a convolution of functions is the product of their transforms.
Reference links
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