Calculate Cosine of a Matrix: Solutions to Systems

  • Context: MHB 
  • Thread starter Thread starter jessicamorgan
  • Start date Start date
  • Tags Tags
    Cosine Matrix
Click For Summary
SUMMARY

The discussion focuses on calculating the cosine of a matrix and its application in solving systems of equations. The cosine of a matrix is defined as cos(A) = I - (1/2!)A² + (1/4!)A⁴ - ..., which behaves similarly to the regular cosine function. Participants clarify that while the matrix cosine definition is important, it primarily serves as a foundation for solving differential equations, particularly y'' = -A²y, where A is a matrix. The conversation emphasizes the relevance of series definitions and term-by-term differentiation in deriving solutions.

PREREQUISITES
  • Understanding of matrix operations and definitions, specifically matrix exponentiation.
  • Familiarity with differential equations, particularly second-order linear equations.
  • Knowledge of Taylor series expansions and their applications in mathematical functions.
  • Basic understanding of trigonometric functions and their matrix counterparts.
NEXT STEPS
  • Study matrix exponentiation techniques and their applications in solving linear systems.
  • Learn about Taylor series and their convergence properties in the context of matrix functions.
  • Explore the derivation of solutions for second-order differential equations involving matrices.
  • Investigate numerical methods for approximating matrix functions, including cosine and sine.
USEFUL FOR

Mathematicians, engineers, and students studying linear algebra and differential equations, particularly those interested in the application of matrix functions in solving complex systems.

jessicamorgan
Messages
5
Reaction score
0
https://uploads.tapatalk-cdn.com/20170308/78feec183e9672f563c5e41b4c52e1d9.jpg

https://uploads.tapatalk-cdn.com/20170308/4ad8560adf9e090969c38515a31d1407.jpg

Please help, I know the definition of a cosine of a matrix is cos(a) = I-1/2!A^2+1/4!A^4-...
But I am unsure how this would help me find solutions to these systems.
 
Physics news on Phys.org
jessicamorgan said:
Please help, I know the definition of a cosine of a matrix is cos(a) = I-1/2!A^2+1/4!A^4-...
But I am unsure how this would help me find solutions to these systems.

Hi jessicamorgan! Welcome to MHB! (Smile)

That is indeed the definition of the cosine of a matrix.
We won't need it other than knowing it exists and behaves like a regular cosine.

Suppose we solve the equation for the 1-dimensional case, when the cosine is really a regular cosine.
What would the solution be?
 
I like Serena said:
Hi jessicamorgan! Welcome to MHB! (Smile)

That is indeed the definition of the cosine of a matrix.
We won't need it other than knowing it exists and behaves like a regular cosine.

Suppose we solve the equation for the 1-dimensional case, when the cosine is really a regular cosine.
What would the solution be?

Hi, thanks for replying.
I'm unsure of the question, I don't understand how to solve or what the cosine has to do with it. :/
 
It looks to me like there are two different ways to look at this problem.
1) That you have already learned that, for numeric functions, the general solution to [math]y''= -A^2y[/math] is $$y(x)= C cos(\sqrt{A}x)+ Dsin(\sqrt{A}x)$$ and are asked to use the series definitions to write that same solution for A a matrix.

2) That you have already learned that you can differentiate such a series "term by term" so that, given [math]y= cos(Ax)= I-1/2!(Ax)^2+1/4!(Ax)^4-...[/math] you have [math]y'= -A(Ax)+ 1/3!A(Ax)^3- ...= -A(Ax- 1/3! (Ax)^3+ ...)[/math] and then [math]y''= -A(A- 1/2!(Ax)^2+ ...)= -A^2y[/math].
 

Similar threads

Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 8 ·
Replies
8
Views
1K
  • · Replies 33 ·
2
Replies
33
Views
2K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K