# expm

Matrix exponential

## Syntax

``Y = expm(X)``

## Description

example

````Y = expm(X)` computes the matrix exponential of `X`. Although it is not computed this way, if `X` has a full set of eigenvectors `V` with corresponding eigenvalues `D`, then ```[V,D] = eig(X)``` andexpm(X) = V*diag(exp(diag(D)))/VUse `exp` for the element-by-element exponential.```

## Examples

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Compute and compare the exponential of `A` with the matrix exponential of `A`.

```A = [1 1 0; 0 0 2; 0 0 -1]; exp(A)```
```ans = 3×3 2.7183 2.7183 1.0000 1.0000 1.0000 7.3891 1.0000 1.0000 0.3679 ```
`expm(A)`
```ans = 3×3 2.7183 1.7183 1.0862 0 1.0000 1.2642 0 0 0.3679 ```

Notice that the diagonal elements of the two results are equal, which is true for any triangular matrix. The off-diagonal elements, including those below the diagonal, are different.

## Input Arguments

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Input matrix, specified as a square matrix.

Data Types: `single` | `double`
Complex Number Support: Yes

## Algorithms

The algorithm `expm` uses is described in  and .

### Note

The files, `expmdemo1.m`, `expmdemo2.m`, and `expmdemo3.m` illustrate the use of Padé approximation, Taylor series approximation, and eigenvalues and eigenvectors, respectively, to compute the matrix exponential. References  and  describe and compare many algorithms for computing a matrix exponential.

 Higham, N. J., “The Scaling and Squaring Method for the Matrix Exponential Revisited,” SIAM J. Matrix Anal. Appl., 26(4) (2005), pp. 1179–1193.

 Al-Mohy, A. H. and N. J. Higham, “A new scaling and squaring algorithm for the matrix exponential,” SIAM J. Matrix Anal. Appl., 31(3) (2009), pp. 970–989.

 Golub, G. H. and C. F. Van Loan, Matrix Computation, p. 384, Johns Hopkins University Press, 1983.

 Moler, C. B. and C. F. Van Loan, “Nineteen Dubious Ways to Compute the Exponential of a Matrix,” SIAM Review 20, 1978, pp. 801–836. Reprinted and updated as “Nineteen Dubious Ways to Compute the Exponential of a Matrix, Twenty-Five Years Later,” SIAM Review 45, 2003, pp. 3–49.