- #1
dreamspace
- 11
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Homework Statement
Homework Equations
Not sure.
The Attempt at a Solution
Have no idea, as I don't have any/much previous experience with Linear Algebra.
Can anyone help me with starting on this, hints/tips?
HallsofIvy said:Surely you can solve [itex]d^2y/dx^2= 1- x[/itex]? Do you know what LU factorization, Gauss-Seidel, etc. are? What is the matrix with n= 4?
dreamspace said:Hi
Yes, I can solve the Differential Equation by hand, and I have some limited knowledge/experience with LU factorization, Gauss-Seidel etc. And matrices in general, but it kinda stops there. I have in general problems understanding how to use everything for the problem, and some of the info included
For example "Xi = i/n is the interior, discrete spatial coordinates on [0,1] with steplength h = 1/n" ? I have no idea what that means, and googling it doesn't come up with a lot either. Neither does searching for Use of sparse matrices and differential equations.
dreamspace said:Thanks. Yes, now I understand the problem. But alas, I'm still not sure how the set it up. I'm understanding (correctly?) that the U vector will be the approximate solutions for the Diff. EQ
Let's take the case of N=4 , would the Matrix equation look like this:
[itex]
n^{2}
\begin{pmatrix}
-2 & 1 & 0 & 0 & \cdots & 0\\
1 & -2 & 1 & 0 & \cdots & 0\\
0 & 1 & -2 & 1 & 0 & 0\\
\vdots & \vdots & 1 & \ddots & \\ \\
0 & 0 & & & & 1\\
0 & 0 & & & 1 & -2\\
\end{pmatrix}
\begin{pmatrix}
u_{1}\\
u_{2}\\
u_{3}\\
\vdots\\
u_{n-1}\\
\end{pmatrix}
=
\begin{pmatrix}
f(x_{1})\\
f(x_{2})\\
f(x_{3})\\
\vdots\\
f(x_{n-1})\\
\end{pmatrix}
\\
\\
\\
4^{2}
\begin{pmatrix}
-2 & 1 & 0\\
1 & -2 & 1\\
0 & 1 & -2
\end{pmatrix}
\begin{pmatrix}
u_{1}\\
u_{2}\\
u_{3}
\end{pmatrix}
=
\begin{pmatrix}
f(x_{1})\\
f(x_{2})\\
f(x_{3})
\end{pmatrix}
\\
\\
\\
\begin{pmatrix}
-32 & 16 & 0\\
16 & -32 & 16\\
0 & 16 & -32
\end{pmatrix}
\begin{pmatrix}
u_{1}\\
u_{2}\\
u_{3}
\end{pmatrix}
=
\begin{pmatrix}
1-\frac{1}{4}\\
1-\frac{2}{4}\\
1-\frac{3}{4}
\end{pmatrix}
\\
\\
\\
\begin{pmatrix}
-32 & 16 & 0\\
16 & -32 & 16\\
0 & 16 & -32
\end{pmatrix}
\begin{pmatrix}
u_{1}\\
u_{2}\\
u_{3}
\end{pmatrix}
=
\begin{pmatrix}
\frac{3}{4}\\
\frac{1}{2}\\
\frac{1}{4}
\end{pmatrix}
[/itex]
?
A sparse matrix is a matrix in which most of the elements are zero. This means that the matrix contains mostly empty or unused space. In contrast, a dense matrix contains mostly non-zero elements.
Sparse matrices are important because they allow for more efficient storage and manipulation of large matrices. Since most of the elements are zero, storing and computing operations on sparse matrices require less memory and computation time compared to dense matrices.
Sparse matrices are often used in fields such as data science, machine learning, and scientific computing. They are particularly useful in problems that involve large amounts of data or require solving systems of linear equations.
A differential equation is a mathematical equation that relates an unknown function to its derivatives. It describes the relationship between a function and its rate of change over time or space.
Differential equations can be solved using linear algebra by converting them into a system of linear equations. This involves representing the derivatives as linear operators and using techniques such as matrix multiplication and Gaussian elimination to solve for the unknown function.