## What does Lu do in Matlab?

## What does Lu do in Matlab?

lu (MATLAB Functions) The lu function expresses a matrix X as the product of two essentially triangular matrices, one of them a permutation of a lower triangular matrix and the other an upper triangular matrix. The factorization is often called the LU, or sometimes the LR, factorization.

## How do you calculate Lu in Matlab?

[ L , U ] = lu( A ) factorizes the full or sparse matrix A into an upper triangular matrix U and a permuted lower triangular matrix L such that A = L*U . [ L , U , P ] = lu( A ) also returns a permutation matrix P such that A = P’*L*U . With this syntax, L is unit lower triangular and U is upper triangular.

**Does all matrix have LU decomposition?**

Do matrices always have an LU decomposition? No. Sometimes it is impossible to write a matrix in the form “lower triangular”×“upper triangular”.

**Does every matrix have an LU decomposition?**

A square matrix is said to have an LU decomposition (or LU factorization) if it can be written as the product of a lower triangular (L) and an upper triangular (U) matrix. Not all square matrices have an LU decomposition, and it may be necessary to permute the rows of a matrix before obtaining its LU factorization.

### What is eye command in MATLAB?

I = eye( n ) returns an n -by- n identity matrix with ones on the main diagonal and zeros elsewhere. example. I = eye( n , m ) returns an n -by- m matrix with ones on the main diagonal and zeros elsewhere. example. I = eye( sz ) returns an array with ones on the main diagonal and zeros elsewhere.

### How do you do a backslash in MATLAB?

MATLAB backslash operator is used to solving a linear equation of the form a*x = b, where ‘a’ and ‘b’ are matrices and ‘x’ is a vector. The solution of this equation is given by x = a \ b, but it works only if the number of rows in ‘a’ and ‘b’ is equal.

**What is the point of LU factorization?**

M = LU is called an LU decomposition of M. This is a useful trick for many computational reasons. It is much easier to compute the inverse of an upper or lower triangular matrix. Since inverses are useful for solving linear systems, this makes solving any linear system associated to the matrix much faster as well.

**Can you do LU factorization on a non square matrix?**

For matrices that are not square, LU decomposition still makes sense. Given an m × n matrix M, for example we could write M = LU with L a square lower unit triangular matrix, and U a rectangular matrix. Then L will be an m × m matrix, and U will be an m × n matrix (of the same shape as M).

#### Does LU factorization always exist?

LUP always exists (We can use this to quickly figure out the determinant). If the matrix is invertible (the determinant is not 0), then a pure LU decomposition exists only if the leading principal minors are not 0.

#### Can you do LU decomposition on a non square matrix?

For matrices that are not square, LU decomposition still makes sense. Given an m × n matrix M, for example we could write M = LU with L a square lower unit triangular matrix, and U a rectangular matrix. From here, the process is exactly the same as for a square matrix.