Example 3: Piecewise Convolution - 13.11 | 13. Convolution Theorem | Mathematics (Civil Engineering -1)
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Interactive Audio Lesson

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Understanding the Functions

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0:00
Teacher
Teacher

Today, we will begin by analyzing two functions: f(t) and g(t). Can anyone explain what a piecewise function is?

Student 1
Student 1

A piecewise function is defined by different expressions based on the input value, right?

Teacher
Teacher

Exactly! So, for our piecewise functions, f(t) is defined as 1 for t between 0 and 1. What about g(t)?

Student 2
Student 2

g(t) is just t, but that means it increases linearly across its range.

Teacher
Teacher

Right! Understanding the definitions is crucial since they'll guide us in computing the convolution.

Calculating the Convolution

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Teacher
Teacher

Let's write down the convolution integral. Who remembers the formula?

Student 3
Student 3

It's the integral of f(τ)g(t-τ) dτ from 0 to t, right?

Teacher
Teacher

Correct! Now, how do we set this up for our specific functions regarding their ranges?

Student 4
Student 4

We consider t values separately! For 0 ≤ t ≤ 1, both functions behave differently compared to when t > 1.

Teacher
Teacher

Exactly! Let's work through Case 1 and establish what (f ∗ g)(t) is for that range.

Case Analysis

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Teacher
Teacher

Now, we've calculated the convolution for t in the first case. What do we get?

Student 1
Student 1

We find (f ∗ g)(t) = t²/2 for 0 ≤ t ≤ 1!

Teacher
Teacher

Perfect! But now, what changes for t > 1?

Student 2
Student 2

Then we only consider f(τ) from 0 to 1 due to its piecewise definition.

Teacher
Teacher

Exactly! Now verifying this integration, we can derive the second part: t - 1/2. What does that lead us to?

Student 3
Student 3

We can compile both results into a piecewise function!

Final Conclusion

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Teacher
Teacher

Alright, can we summarize the final piecewise result that we obtained?

Student 4
Student 4

Sure! (f ∗ g)(t) = t²/2 for 0 ≤ t ≤ 1 and t - 1/2 for t > 1!

Teacher
Teacher

Well articulated! This clearly demonstrates how function behavior affects convolution. Well done!

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section illustrates the process of piecewise convolution using functions defined over specific intervals, detailing each step involved in the calculations.

Standard

In this section, we explore the example of piecewise convolution between two functions: f(t), defined as 1 for 0≤t≤1, and g(t), defined as t for the same interval. The convolution is computed for two cases, where the ranges of t differ, illustrating the integral calculations distinctly for the two scenarios.

Detailed

Example 3: Piecewise Convolution

In this section, we analyze the convolution of two piecewise functions, f(t) and g(t), specifically designed to demonstrate how piecewise definitions impact the convolution process:

  • f(t) is defined as:

$$
f(t) = \begin{cases}
1, & 0 \leq t \leq 1 \
0, & t > 1
\end{cases}
$$

  • g(t) is defined as:

$$
g(t) = t
$$

The goal is to compute the convolution of f and g, symbolized as (f ∗ g)(t).

Finding (f ∗ g)(t)

The formula for convolution is given by:

$$
(f ∗ g)(t) = \int_{0}^{t} f(\tau)g(t - \tau)d\tau
$$

In solving this, we need to consider two scenarios based on the piecewise nature of f(t):

  1. Case 1: 0 ≤ t ≤ 1
  2. For this scenario, f(\tau) equals 1 for all \tau within the limits of integration:

$$
(f ∗ g)(t) = \int_{0}^{t} (1)(t - \tau) d\tau = \int_{0}^{t} (t - \tau) d\tau
$$
- Evaluating this integral yields:

$$
(f ∗ g)(t) = \left[ t\tau - \frac{\tau^2}{2} \right]_{0}^{t} = tt - \frac{t^2}{2} = \frac{t^2}{2}
$$

  1. Case 2: t > 1
  2. In this case, f(\tau) remains equal to 1 only from τ=0 to τ=1. Therefore, the limits of the integral adjust accordingly:

$$
(f ∗ g)(t) = \int_{0}^{1}(1)(t - \tau) d\tau = \left[ t\tau - \frac{\tau^2}{2} \right]_{0}^{1}
$$
- This results in:

$$
(f ∗ g)(t) = (t)(1) - \frac{(1)^2}{2} = t - \frac{1}{2}
$$

Piecewise Result

Combining both cases, we can express the final result of the convolution as a piecewise function:

$$
(f ∗ g)(t) = \begin{cases}
\frac{t^2}{2}, & 0 \leq t \leq 1 \
t - \frac{1}{2}, & t > 1
\end{cases}
$$

This example illustrates the importance of considering the nature of the functions when performing convolution, particularly when applying it to real-world engineering scenarios.

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Audio Book

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Defining Functions f(t) and g(t)

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Let:

$$
f(t)=\begin{cases}
1, & 0 \leq t \leq 1 \
0, & t > 1
\end{cases}$$

$$
g(t)=t$$

Detailed Explanation

In this example, we have two functions. The function f(t) is defined as 1 between time 0 and 1, and 0 afterwards, which means it only has a significance in that small time window. On the other hand, g(t) is simply the function that equals t, meaning its value increases constantly as time progresses. These functions will be used to calculate their convolution over different time intervals.

Examples & Analogies

Imagine f(t) as a light switch that is turned on (value 1) only for the first second of a process, representing a brief burst of energy, while g(t) represents a continuously increasing temperature gauge. During the brief moment when the switch is on, we will analyze how that quick burst affects the temperature gauge over time.

Calculating the Convolution for Case 1 (0 ≤ t ≤ 1)

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We compute:
$$
\int_0^t (f \ast g)(t)= \int_0^t f(\tau) g(t-\tau) d\tau
$$
Since f(\tau)=1 for \tau \in[0,t]:

$$
\int_0^t (t-\tau) d\tau = \frac{t^2}{2}$$

Detailed Explanation

In this case (when t is between 0 and 1), we substitute f(τ) = 1, simplifying our integral to just g(t - τ) over the range from 0 to t. This results in the integral that computes the area under the graph of g(t) from 0 to t, giving us \( \frac{t^2}{2} \), which captures the cumulative effect of g(t) during this time period.

Examples & Analogies

Think of this as pouring a little bit of syrup (g(t)) into a container (the integral) every second for the first one second. The total volume of syrup collected in that second is represented by \( \frac{t^2}{2} \) - showing how much can accumulate even in that short burst.

Calculating the Convolution for Case 2 (t > 1)

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Now f(\tau)=1 only from \tau =0 to 1:
$$
\int_0^1 (t-\tau) d\tau = t\tau - \frac{\tau^2}{2} \Big|_0^1 = t - \frac{1}{2}$$

Detailed Explanation

In this case (when t is greater than 1), f(τ) remains 1 only from 0 to 1, while g(t - τ) adjusts accordingly. The integral thus computes the area under g(t) again, but this time the upper limit of the integral is capped at 1, reflecting that f(τ) is not active beyond that point. The result is \( t - \frac{1}{2} \), indicating how the initial burst (from f(t)) has an effect even after it has turned off.

Examples & Analogies

Imagine a hose (g(t)) which starts spraying water continuously after the switch is pushed. Even after the brief activation of the switch, the water sprays for a while, but it is limited by the initial pressure (1 unit of f(τ)) established only for a short moment. As time passes beyond that initial burst, the total effect on the system can be computed until the constraints of the burst influence the overall outcome.

Final Results of the Convolution

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Thus:
$$
(f \ast g)(t)=\begin{cases}
t^2, & 0 \leq t \leq 1 \
t - \frac{1}{2}, & t > 1\end{cases}$$

Detailed Explanation

The final result encapsulates everything we've discussed in the previous chunks. It summarizes the impact of both functions through time, reflecting how their interactions yield different results depending on the interval being analyzed. During the onset (0 ≤ t ≤ 1), the effect is quadratic due to the consistent influence of f(t). Beyond that, the growth pattern changes due to the diminishing influence of f(t), giving us a linear effect based on the performance of g(t).

Examples & Analogies

This final expression can be seen as the overall temperature perceived in a room where warm energy was rapidly introduced for just a moment. Initially, during the effective input time, the temperature rises quite dramatically, followed by a gradual increase as the room continues to heat with time. By summarizing the impact mathematically, we can better predict and analyze behaviors in a variety of systems.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Piecewise Convolution: The operation defining the output as a combination of integrals based on the definitions of each segment of the functions.

  • Integral Limits: Distinct intervals must be considered based on the piecewise nature of the functions.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example of the convolution of f(t)=1 (0≤t≤1) and g(t)=t, yielding different results based on the value of t.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • For f(t) that's one in a span, Convolution helps us understand!

📖 Fascinating Stories

  • Once, there were functions f and g that only worked together in their defined ranges. They combined through a magical integral to form a new existence.

🧠 Other Memory Gems

  • Fabulous Integrals Produce Results - Remember that convolution requires integrating each piece appropriately.

🎯 Super Acronyms

CPR (Convolution, Piecewise, Result) - Remember the process of convolution in piecewise functions.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Convolution

    Definition:

    A mathematical operation that blends two functions, such as f(t) and g(t), to produce a new function representing their overlap.

  • Term: Piecewise function

    Definition:

    A function defined by multiple segments, each applicable to a specific interval of the input variable, often denoted as f(t).