expm {Matrix} | R Documentation

## Matrix Exponential

### Description

Compute the exponential of a matrix.

### Usage

    expm(x)

### Arguments

`x` | a matrix, typically inheriting from the `dMatrix` class.

### Details

The exponential of a matrix is defined as the infinite Taylor series `expm(A) = I + A + A^2/2! + A^3/3! + ...` (although this is definitely not the way to compute it). The method for the `dgeMatrix` class uses Ward's diagonal Pade' approximation with three step preconditioning.

### Value

The matrix exponential of `x`.

### Author(s)

This is a translation of the implementation of the corresponding Octave function contributed to the Octave project by A. Scottedward Hodel A.S.Hodel@Eng.Auburn.EDU. A bug in there has been fixed by Martin Maechler.

### References

http://en.wikipedia.org/wiki/Matrix_exponential

Cleve Moler and Charles Van Loan (2003) Nineteen dubious ways to compute the exponential of a matrix, twenty-five years later. SIAM Review 45, 1, 3–49.

Eric W. Weisstein et al. (1999) Matrix Exponential. From MathWorld, http://mathworld.wolfram.com/MatrixExponential.html

### See Also

`Schur`

### Examples

    (m1 <- Matrix(c(1,0,1,1), nc = 2))
    (e1 <- expm(m1)) ; e <- exp(1)
    stopifnot(all.equal(e1@x, c(e,0,e,e), tol = 1e-15))
    (m2 <- Matrix(c(-49, -64, 24, 31), nc = 2))
    (e2 <- expm(m2))
    (m3 <- Matrix(cbind(0,rbind(6*diag(3),0))))# sparse!
    (e3 <- expm(m3)) # upper triangular

[Package Matrix version 0.999375-33 Index]