Implicit numerical differentiation

In summary, the conversation is about using the Crank-Nicolson method to solve a logistic function for population growth. The problem arises when solving for the next time step, as there are two solutions for the value of u_{n+1}. The question is whether this signifies an error in the method or if one of the solutions can be chosen based on its proximity to the previous value, u_n. The equation being used is an implicit scheme for logistic growth with a carrying capacity, R.
  • #1
MaxManus
277
1

Homework Statement



I am using Crank–Nicolson to solve a logistic function, modeling population growth.
To get the next time step, I have to solve a quadratic equation.
The problem is that i get two solutions for y(i+1). Does it mean that I am doing it wrong?
If not, can I just pick the solution that is closest to y(i)?
 
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  • #2
Example:
Logistic growth, implicit scheme, not Crank-Nicolson.

[tex]\frac{u_{n+1}-u_n}{\Delta t} = n_{n+1}(1 - \frac{u_{n+1}}{R})[/tex]

R is the carrying capacity

Here I have to solve a quadratic equation to find [tex] u_{n+1}[/tex]
 

1. What is implicit numerical differentiation?

Implicit numerical differentiation is a technique used in mathematical modeling to estimate the derivative of a function at a given point. It involves using various numerical methods to approximate the derivative without having an explicit formula for the function.

2. How does implicit numerical differentiation differ from explicit numerical differentiation?

Explicit numerical differentiation involves using a formula or algorithm to directly calculate the derivative at a point, while implicit numerical differentiation uses iterative methods to approximate the derivative without an explicit formula.

3. What are the advantages of using implicit numerical differentiation?

Implicit numerical differentiation can be more accurate and stable than explicit methods, especially when dealing with functions that have complex or discontinuous behavior. It also allows for the estimation of derivatives for functions that do not have an explicit formula.

4. What are some common numerical methods used in implicit numerical differentiation?

Some common methods include the Newton-Raphson method, the secant method, and the Gauss-Newton method. These methods use a combination of function evaluations and approximations to iteratively estimate the derivative.

5. What are some applications of implicit numerical differentiation in scientific research?

Implicit numerical differentiation is used in a variety of fields, such as physics, engineering, economics, and computer science. It can be used to analyze and optimize complex systems, solve differential equations, and estimate the sensitivity of a system to changes in its parameters.

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