Ops functions for units objects, including comparison, product and divide, add, subtract.

## Arguments

- e1
object of class

`units`

, or something that can be coerced to it by`as_units(e1)`

- e2
object of class

`units`

, or something that can be coerced to it by`as_units(e2)`

, or in case of power a number (integer n or 1/n)

## Details

Users are advised against performing arithmetical operations with temperatures in different units. The units package ensure that results 1) are arithmetically correct, and 2) satisfy dimensional analysis, but could never ensure that results are physically meaningful. Temperature units are special because there is an absolute unit, Kelvin, and relative ones, Celsius and Fahrenheit degrees. Arithmetic operations between them are meaningless from the physical standpoint. Users are thus advised to convert all temperatures to Kelvin before operating.

## Examples

```
a <- set_units(1:3, m/s)
b <- set_units(1:3, m/s)
a + b
#> Units: [m/s]
#> [1] 2 4 6
a * b
#> Units: [m^2/s^2]
#> [1] 1 4 9
a / b
#> Units: [1]
#> [1] 1 1 1
a <- as_units("kg m-3")
b <- set_units(1, kg/m/m/m)
a + b
#> 2 [kg/m^3]
a = set_units(1:5, m)
a %/% a
#> Units: [1]
#> [1] 1 1 1 1 1
a %/% set_units(2)
#> Units: [m]
#> [1] 0 1 2 2 2
set_units(1:5, m^2) %/% set_units(2, m)
#> Units: [m]
#> [1] 0 1 2 2 2
a %% a
#> Units: [m]
#> [1] 0 0 0 0 0
a %% set_units(2)
#> Units: [m]
#> [1] 1 0 -1 0 1
```