[R] Vorticity and Divergence

[Ravi Varadhan]

Both vorticity and divergence are defined in terms of partial derivatives.
You can compute these derivatives using the `grad' function in "numDeriv"
package.

U <- function(X) { your U function}
V <- function(X) { your V function} 
# where X = c(x,y)

library(numDeriv)

grU <- function(X) grad(X, func=U)
grV <- function(X) grad(X, func=V)

# For a 2-dimensional vector field

vortivcity <- function(X) grV(X)[2] - grU(X)[1]
divergence <- function(X) grU(X)[1] + grV(X)[2]


# Here is an example:

U <- function(X) X[1]^2 + X[1] * X[2]
V <- function(X) X[2]^2 - X[1] * X[2]

> vorticity(c(2,1))
[1] -5
> divergence(c(2,1))
[1] 5
>

Does this help?

Ravi.
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Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health

Division of Geriatric Medicine and Gerontology 

Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan at jhmi.edu

Webpage:  http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html

 

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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Igor Oliveira
Sent: Monday, September 08, 2008 11:37 AM
To: r-help at r-project.org
Subject: [R] Vorticity and Divergence

Hi all,

I have some wind data (U and V components) and I would like to compute
Vorticity and Divergence of these fields. Is there any R function that can
easily do that?

Thanks in advance for any help

Igor Oliveira
CSAG, Dept. Environmental & Geographical Science, University of Cape Town,
Private Bag X3, Rondebosch 7701. Tel.: +27 (0)21 650 5774
South Africa             Fax: +27 (0)21 650 5773
      http:///www.csag.uct.ac.za/~igor

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