Extract: Extract or replace parts of three-velocity

In lorentz: The Lorentz Transformation in Relativistic Physics

Extract or replace parts of three-velocity

Description

Extract or replace subsets of three-velocities

Usage

## S3 method for class 'vec'
x[i, j, drop=TRUE, ...]
## S3 replacement method for class '3vel'
x[i, j] <-  value
## S3 replacement method for class '4vel'
x[i, j] <-  value

Arguments

x	A three-vector
i, j	elements to extract or replace
value	replacement value
drop	Boolean, with default TRUE meaning to drop values
...	Further arguments, currently ignored

Details

These methods (should) work as expected: an object of class 3vel is a three-column matrix with rows corresponding to three-velocities; a single argument is interpreted as a row number. Salient use-cases are u[1:5] <- u[1] and u[1] <- 0.

To extract a single component, pass a second index: u[,1] returns the x- component of the three-velocity.

Extraction functions take a drop argument, except for x[i] which returns a vec object.

Currently, u[] returns u but I am not sure this is desirable. Maybe it should return unclass(u) or perhaps c(unclass(u)).

Use idiom u[] <- x to replace entries of u elementwise.

Examples

u <- r3vel(10)
u[1:4]
u[5:6] <- 0

u[7:8] <- u[1]

u[,1] <- 0.1

lorentz documentation built on July 20, 2026, 5:08 p.m.