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Last data update: 2014.03.03

R: Expokit __EXPV and __PHIV wrapper.

Rexpv

R Documentation

Expokit EXPV and PHIV wrapper.

Description

R wrapper of the Expokit Fortran subroutines __EXPV and __PHIV for sparse matrix exponentiation. In general, these routines compute the solution at time point t of the ODE

w'(t) = x w(t) + u

with initial condition w(0) = v.

Usage

  Rexpv(a, ia, ja, n, v, t = 1, storage = "CCS", u = NULL,
    anorm = max(abs(a)), Markov = FALSE, m = 30L, tol = 0,
    itrace = 0L, mxstep = 10000L)

Arguments

`a`	`numeric` or `complex` non-zero entries in the x-matrix.
`ia`	`integer` index/pointer. Precise meaning depends on storage format.
`ja`	`integer` index/pointer. Precise meaning depends on storage format.
`n`	dimension of the (square) matrix.
`v`	`numeric` or `complex` vector.
`t`	time. Default `1`.
`storage`	`character`, one of `'CCS'` (Compressed Column Storage), `'CRS'` (Compressed Row Storage) or `'COO'` (COOrdinate list). Default `'CCS'`.
`u`	`numeric` or `complex` vector. Default `NULL`.
`anorm`	A norm of the matrix. Default is the sup-norm.
`Markov`	`logical`, if `TRUE` the (transposed) matrix is taken to be an intensity matrix and steps are taken to ensure that the computed result is a probability vector. Default `FALSE`.
`m`	`integer`, the maximum size for the Krylov basis.
`tol`	`numeric`. A value of 0 (default) means square root of machine eps.
`itrace`	`integer`, 0 (default) means no trace information from Expokit, 1 means print 'happy breakdown', and 2 means all trace information printed from Expokit.
`mxstep`	`integer`. Maximum allowable number of integration steps. The value 0 means an infinite number of steps. Default 10000.

Details

The Rexpv function is the low level wrapper of the Fortran subroutines in the Expokit package. It is not intended to be used directly but rather via the expv methods. In the call the correct storage format in terms of the vectors a, ia and ja has to be specified via the storage argument. For CCS, ia contains 1-based row numbers of non-zero elements and ja contains 1-based pointers to the initial element for each column. For CRS, ja contains 1-based column numbers of non-zero elements and ia are 1-based pointers to the initial element for each row. For COO, ia and ja contain the 1-based column and row numbers, respectively, for the non-zero elements.

Value

The solution, w, of the ODE as a numeric or complex vector of length n.

Author(s)

Niels Richard Hansen Niels.R.Hansen@math.ku.dk

References

Sidje, R. B. (1998) Expokit. Software Package for Computing Matrix Exponentials. ACM Trans. Math. Softw. 24(1), 130-156.

Examples

### A CCS 4 by 4 real matrix. The last element in 'ja' is the number of
### non-zero elements + 1.
a <- c(-1, 1, -2, -3, 1, 2, -1)
ia <- c(1, 3, 2, 4, 1, 2, 3)
ja <- c(1, 3, 5, 6, 8)

v <- c(1, 1, 1, 1)
wCCS <- expoRkit:::Rexpv(a, ia, ja, 4, v = v)

### COO storage instead.
ja <- c(1, 1, 2, 2, 3, 4, 4)
wCOO <- expoRkit:::Rexpv(a, ia, ja, 4, v = v, storage = 'COO')

### CRS storage instead.
a <- c(-1, 1, -2, 2, 1, -1, -3)
ja <- c(1, 3, 2, 4, 1, 4, 2)
ia <- c(1, 3, 5, 7, 8)
wCRS <- expoRkit:::Rexpv(a, ia, ja, 4, v = v, storage = 'CRS')

cbind(wCCS, wCOO, wCRS)

stopifnot(all.equal(wCCS, wCOO),
          all.equal(wCCS, wCRS),
          all.equal(wCRS, wCOO))

## Complex version
a <- c(-1, 1i, -2, -3i, 1, 2i, -1)
ia <- c(1, 3, 2, 4, 1, 2, 3)
ja <- c(1, 3, 5, 6, 8)

v <- c(1, 1, 1, 1)
wCCS <- expoRkit:::Rexpv(a, ia, ja, 4, v = v)

### COO storage instead.
ja <- c(1, 1, 2, 2, 3, 4, 4)
wCOO <- expoRkit:::Rexpv(a, ia, ja, 4, v = v, storage = 'COO')

### CRS storage instead.
a <- c(-1, 1, -2, 2i, 1i, -1, -3i)
ja <- c(1, 3, 2, 4, 1, 4, 2)
ia <- c(1, 3, 5, 7, 8)
wCRS <- expoRkit:::Rexpv(a, ia, ja, 4, v = v, storage = 'CRS')

cbind(wCCS, wCOO, wCRS)

stopifnot(all.equal(wCCS, wCOO),
          all.equal(wCCS, wCRS),
          all.equal(wCRS, wCOO))