Question on Ordinary Differential Equation (ODE)

But d/dx (-u) = -du/dx.So the two are equal if and only if d2u/dy2 = 0, which means u = Ay + B. That's what you get from solving (1).In summary, the conversation discusses finding the ODE for two different equations, (1) and (2), and the solutions for each. It is noted that (2) is a partial differentiation with respect to x, so any additive term dependent on y will disappear. The solution for (1) is u = A(x)e^(-y), while the solution for (2) is u = e^(-y)(B(x) + c(y)). The conversation then explores the reasoning
  • #1
a150daysflood
23
0

Homework Statement



Find the ODE of the following
(1) du/dy = -u
(2) d^2u/dxdy = -du/dx


Homework Equations



For question 1, the answer is u= A(x)e^(-y)
while for question 2, the answer is u= e^(-y)(B(X) + c(Y))


The Attempt at a Solution



I've already solved the question, but just want to ask, if i change (1) to (2), its just a differentiation with respect to dx, but yet the solution contain a c(Y) term, any idea why is this so?
 
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  • #2
To get those answers, these are PDEs, surely?
In (2), both sides have been differentiated partially wrt x. So any additive term that depends solely on y will have disappeared and cannot be reconstructed from the PDE. It's analogous to the constant of integration in ODEs.
 
  • #3
If you differentiate (1) wrt x, then
d/dx (du/dy) = d/dy (du/dy) dy/dx = d2u/dy2 dy/dx, by chain rule.
 

1. What is an ordinary differential equation (ODE)?

An ordinary differential equation (ODE) is a mathematical equation that describes the relationship between a function and its derivatives. It involves one or more independent variables and their derivatives with respect to the dependent variable.

2. What are some real-world applications of ODEs?

ODEs have a wide range of applications in fields such as physics, engineering, economics, and biology. Some examples include modeling population growth, predicting the motion of a pendulum, and analyzing the behavior of electrical circuits.

3. How do you solve an ODE?

The method for solving an ODE depends on its type and complexity. Some common techniques include separation of variables, using integrating factors, and using power series. There are also numerical methods that can be used to approximate solutions.

4. What is the difference between an ordinary differential equation and a partial differential equation?

The main difference between an ordinary differential equation and a partial differential equation is the number of independent variables involved. ODEs involve only one independent variable, while PDEs involve two or more. PDEs are also more complex and require different methods for solving.

5. How are ODEs used in machine learning and data analysis?

In machine learning and data analysis, ODEs can be used to model and make predictions about dynamic systems. They can also be used for feature extraction, data smoothing, and dimensionality reduction. ODE-based models are often used in time series analysis and forecasting.

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