Charpit’s Equations - 6.3 | 6. Charpit’s Method | Mathematics - iii (Differential Calculus) - Vol 2
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6.3 - Charpit’s Equations

Practice

Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Introduction to Charpit’s Method

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0:00
Teacher
Teacher

Today, we will discuss Charpit's Method, a powerful technique for solving first-order non-linear PDEs. Can anyone tell me what a PDE is?

Student 1
Student 1

A PDE is a partial differential equation, which involves functions of several variables and their partial derivatives.

Teacher
Teacher

That's correct! Specifically, what we deal with in Charpit's Method is of the form F(x, y, z, p, q) = 0, where p and q are the derivatives of z with respect to x and y. Can anyone explain how we represent p and q?

Student 2
Student 2

p is equal to the partial derivative of z with respect to x, and q is the partial derivative with respect to y.

Teacher
Teacher

Great! Now, Charpit's method is especially useful when the PDEs cannot be solved by standard methods. Remember this acronym: C.O.R.E. — it stands for Convert, Obtain, Represent, and Extract. Let's move on!

Understanding Charpit’s Equations

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0:00
Teacher
Teacher

Let’s discuss Charpit's equations. These comprise a system of differential equations derived from the PDE. Can anyone summarize these equations?

Student 3
Student 3

They are dx/dt = ∂F/∂p, dy/dt = ∂F/∂q, and others that relate p and q to the function F.

Teacher
Teacher

Exactly! The relationships you mentioned help to reduce the PDE into simpler ODEs. What do you think is the significance of these transformations?

Student 4
Student 4

It allows us to find solutions that might be hard to get directly from the original PDE.

Teacher
Teacher

Perfectly said! Remember the acronym D.A.R.E. — Differentiate, Apply, Reformulate, Evaluate when solving problems with Charpit's equations.

Steps to Solve Using Charpit’s Method

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0:00
Teacher
Teacher

Now, let’s go through the steps to apply Charpit's Method. Who can list the first step?

Student 1
Student 1

Start with the given PDE: F(x, y, z, p, q) = 0.

Teacher
Teacher

Right! After that, what comes next?

Student 3
Student 3

We calculate the partial derivatives of F.

Teacher
Teacher

Exactly! And after obtaining these derivatives, then what?

Student 2
Student 2

We write the Charpit's auxiliary equations.

Teacher
Teacher

Well done! By solving the ODE system, we can find p and q. Remember, the mnemonic 'I.S.O' — Integrate, Substitute, Obtain helps in remembering the final integration step to find z.

Example Problem

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0:00
Teacher
Teacher

Let’s solve an example using Charpit’s Method. Can anyone tell what the first step is with our PDE z = px + qy + pq?

Student 4
Student 4

We need to convert it into its standard form as F(x, y, z, p, q) = 0.

Teacher
Teacher

Correct! What do we have then?

Student 1
Student 1

F(x, y, z, p, q) = px + qy + pq - z = 0.

Teacher
Teacher

Excellent! Now, who will remind us of the next steps, especially in regard to calculating the partials?

Student 3
Student 3

We compute the necessary partial derivatives of F.

Teacher
Teacher

Exactly, and then we can write the Charpit’s equations. Does anyone remember how these were structured?

Student 2
Student 2

They relate to F's partial derivatives with respect to p, q, x, and y.

Teacher
Teacher

Great! This interaction highlights key points step-by-step and solidifies your understanding of the method.

Introduction & Overview

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

Quick Overview

Charpit’s Equations provide a systematic technique for solving first-order non-linear partial differential equations (PDEs).

Standard

In this section, we explore Charpit’s Method, a powerful approach to solve first-order non-linear PDEs by transforming them into a system of ordinary differential equations (ODEs) through auxiliary equations, ultimately to find their complete integral.

Detailed

Charpit’s Method

Charpit’s Method, named after the French mathematician Jean Charpit, is particularly effective for solving first-order non-linear partial differential equations (PDEs) of the form:

F(x, y, z, p, q) = 0

where:
- z is the unknown function dependent on x and y,
- p = ∂z/∂x, q = ∂z/∂y.

This method stands out when standard techniques like the method of characteristics or Lagrange’s method are insufficient. The fundamental objectives of Charpit’s Method include:
- Finding the complete integral of a first-order non-linear PDE.
- Reformulating the PDE into a set of ordinary differential equations (ODEs) that can be solved to derive a solution.

Charpit’s Equations

Starting with the PDE: F(x, y, z, p, q) = 0, Charpit's equations comprise the following relationships:

  • dx/dt = ∂F/∂p
  • dy/dt = ∂F/∂q
  • dz/dt = p * ∂F/∂p + q * ∂F/∂q - ∂F/∂x - p * ∂F/∂z
  • dp/dt = -∂F/∂y - q * ∂F/∂z

Through solving this system of five differential equations, we can obtain the general or complete integral of a PDE.

Steps to Solve a PDE Using Charpit’s Method

  1. Start with the given PDE: F(x, y, z, p, q) = 0.
  2. Compute the necessary partial derivatives of F.
  3. Establish the Charpit's auxiliary equations.
  4. Solve the resulting system of ODEs.
  5. Extract expressions for p and q:
  6. Integrate to find the complete integral z(x, y).

Example Problem

An illustrative example demonstrates the entire process, where the given PDE is solved through a clear, step-by-step application of Charpit’s Method. This example not only reinforces practical application but also elucidates each step needed to translate the PDE into its solution.

Conclusion

Charpit's method offers a reliable route to tackle first-order non-linear PDEs, especially when traditional methods reveal inadequate.

Youtube Videos

But what is a partial differential equation?  | DE2
But what is a partial differential equation? | DE2

Audio Book

Dive deep into the subject with an immersive audiobook experience.

Introduction to Charpit's Equations

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Given a first-order PDE:
𝐹(𝑥,𝑦,𝑧,𝑝,𝑞) = 0
Define:
• 𝑝 = ∂𝑧/∂𝑥
• 𝑞 = ∂𝑧/∂𝑦

Detailed Explanation

In this chunk, we start with a first-order partial differential equation (PDE) represented by F(x, y, z, p, q) = 0. Here, z is an unknown function of x and y. The terms p and q are defined as the partial derivatives of z with respect to x and y, respectively. This allows us to relate the changes in z to the changes in the independent variables x and y.

Examples & Analogies

Think of a mountain where the height (z) at any point depends on the coordinates (x, y). The slopes in the x and y directions (p and q) tell us how steep the mountain is at that location. In mathematics, just as we can express the height of a mountain in terms of its coordinates, we express z in terms of x, y, and its slopes.

Charpit's Equations

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Then, Charpit's equations are:
𝑑𝑥/∂𝐹/∂𝑝 = 𝑑𝑦/∂𝐹/∂𝑞 = 𝑑𝑧/(𝑝 ⋅ ∂𝐹/∂𝑝 + 𝑞 ⋅ ∂𝐹/∂𝑞 − ∂𝐹/∂𝑥 − 𝑝 ⋅ ∂𝐹/∂𝑧)
𝑑𝑞 = −(∂𝐹/∂𝑦 + 𝑞 ⋅ ∂𝐹/∂𝑧)

Detailed Explanation

This chunk presents Charpit's equations which form a system of differential equations derived from our original PDE. Each part of the equation represents how changes in one variable (x, y, z, p, or q) relate to changes in another. The equations indicate a relationship between the independent variables and the derivatives of F, expressing them in a coherent mathematical system.

Examples & Analogies

Imagine navigating through a multi-dimensional landscape, where each equation in Charpit's system represents a path to take based on the slope and direction of the terrain. By following these paths, you can find a way through that guides you to the solution of the original problem, just like following a map to reach a destination.

Five Differential Equations

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This gives us a system of five differential equations, and the solution of this system provides us with the general or complete integral of the PDE.

Detailed Explanation

In this part, it is highlighted that the system created by Charpit's equations consists of five differential equations. Solving these equations simultaneously leads us to find the complete integral of our original PDE. This means we can obtain a general solution that encompasses all possible solutions of the PDE.

Examples & Analogies

Consider a five-way intersection in a city. Each road represents one of the differential equations. To get to your destination (the solution), you need to navigate through this intersection correctly, understanding the directions supported by each equation, ensuring you arrive at the right path.

Steps to Solve a PDE Using Charpit’s Method

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  1. Start with the given PDE: 𝐹(𝑥,𝑦,𝑧,𝑝,𝑞) = 0
  2. Calculate the partial derivatives:
    • ∂𝐹/∂𝑥
    • ∂𝐹/∂𝑦
    • ∂𝐹/∂𝑧
    • ∂𝐹/∂𝑝
    • ∂𝐹/∂𝑞
  3. Write the Charpit's auxiliary equations using:
    𝑑𝑥/𝐹 = 𝑑𝑦/𝐹 = 𝑑𝑧/(p𝐹 + q𝐹 −𝐹 − p𝐹 − 𝐹 − q𝐹)
  4. Solve the system of ODEs using any possible combination of equations.
  5. Find the expressions for p and q in terms of x,y,z.
  6. Integrate to obtain the complete integral (general solution) z(x,y).

Detailed Explanation

This chunk provides a step-by-step approach for applying Charpit's Method to solve a PDE. It emphasizes the need to start from the original PDE, calculate required derivatives, set up the auxiliary equations, and then solve the resulting ordinary differential equations (ODEs). Finally, it explains how to achieve the complete integral as the solution to the PDE.

Examples & Analogies

Imagine assembling a bicycle from a set of parts. Each step you take corresponds to a step in the Charpit’s Method: starting with all the components (the PDE), understanding how they fit together (the derivatives), assembling the framework (the auxiliary equations), and attaching the wheels and brakes (solving the ODEs) until you finally have a fully functional bike ready to ride (the complete integral).

Definitions & Key Concepts

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

Key Concepts

  • Charpit’s Method: A systematic technique to solve first-order non-linear PDEs by converting them into ODEs.

  • Auxiliary Equations: Equations used to simplify the process of finding a solution to a PDE.

  • Complete Integral: The final result of the method, representing the general solution.

Examples & Real-Life Applications

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

Examples

  • An example where the PDE z = px + qy + pq is solved step by step using Charpit’s Method.

Memory Aids

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

🎵 Rhymes Time

  • 'Convert it, obtain the relation, Represent well, extract to the station!'

📖 Fascinating Stories

  • Imagine Charpit as a hero who transforms tricky PDEs into simple paths (ODEs) to lead to treasure (solutions).

🧠 Other Memory Gems

  • The mnemonic C.O.R.E. stands for: Convert, Obtain, Represent, Extract.

🎯 Super Acronyms

D.A.R.E. = Differentiate, Apply, Reformulate, Evaluate.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Partial Differential Equation (PDE)

    Definition:

    An equation that involves functions of several variables and their partial derivatives.

  • Term: Auxiliary Equations

    Definition:

    Equations derived from a PDE that help reduce it into a system of ordinary differential equations (ODEs).

  • Term: Complete Integral

    Definition:

    The general solution of a PDE found after solving the auxiliary equations.

  • Term: Ordinary Differential Equations (ODEs)

    Definition:

    Differential equations containing one independent variable and one or more dependent variables.

  • Term: Jean Charpit

    Definition:

    A French mathematician known for developing Charpit’s Method for solving non-linear PDEs.