The Units:-Simple subpackage provides an environment that allows users to work with units in their computations. The with(Units:-Simple) command establishes an environment in which some functions, including the ones for basic arithmetic, are modified to accept input with units. By default, the with(Units) command does the same.

Every command in the Simple Units environment that needs to determine whether an expression is valid or not, does so using the Units:-TestDimensions command.

To use the Simple Units environment, enter units using the Unit command, *Unit(unit_name).

In the Simple Units environment, in contrast to the Standard and Natural environments, unassigned variables are not automatically assumed to represent unit-free quantities. For example, $5⟦m⟧+x$ is a valid expression if $x$ is unassigned, because $x$ may represent a length. On the other hand, $\left(5⟦m⟧+x\right)\left(6⟦s⟧+x\right)$ is an invalid expression, because the first factor implies that $x$ represents a length, whereas the second factor implies that $x$ is a duration.

In the Simple Units environment, any verifications of valid dimensions ignore so-called Unit annotations. As a consequence, for example, you can add angles to unit-free quantities.

When using the Units:-Simple package, units will by default be converted to your selected unit system. (The default system is SI, the metric system.) To change the default system of units, use the UseSystem command.

The with(Units:-Simple) command does not allow the use of the short form of the Units package commands that customize the dimensions, units, and systems of units. In order to do that, it is necessary to enter the with(Units) command (which, by default, also loads the Units:-Simple package). For a list of the commands in the Units package, see Units.

To enter a unit in 2-D Math input, select the unit from the appropriate Units palette. If the unit you want is not there, select $\mathrm{unit}$ and then enter the unit.

When you edit a unit, double brackets appear around it.

$\mathrm{with}\left(\mathrm{Units}:-\mathrm{Simple}\right)\:$

$\mathrm{a\_length}≔2\mathrm{Unit}\left('m'\right)$

$\mathrm{a\_length}≔2⟦m⟧$

$\mathrm{a\_width}≔3\mathrm{Unit}\left('m'\right)$

$\mathrm{a\_width}≔3⟦m⟧$

$\mathrm{an\_area}≔\mathrm{a\_length}\mathrm{a\_width}$

$\mathrm{an\_area}≔6⟦m^2⟧$

$3x^4\mathrm{Unit}\left('\mathrm{ft}'\right)+4xy{\left(y-x\right)}^2\mathrm{Unit}\left('\mathrm{ft}'\right)$

$\left(3x^4+4xy{\left(y-x\right)}^2\right)⟦\mathrm{ft}⟧$

$3x^4\mathrm{Unit}\left('m'\right)+4xy{\left(y-x\right)}^2\mathrm{Unit}\left('\mathrm{ft}'\right)$

$\left(3x^4+\frac{762xy{\left(y-x\right)}^2}{625}\right)⟦m⟧$

$\mathrm{diff}\left(\,x\mathrm{Unit}\left('s'\right)\right)$

$\left(12x^3+\frac{762y{\left(y-x\right)}^2}{625}-\frac{1524xy\left(y-x\right)}{625}\right)⟦\frac{m}{s}⟧$

$\mathrm{collect}\left(\,x\right)$

$\left(12x^3+\frac{2286}{625}y{x}^2-\frac{3048}{625}{y}^{2}x+\frac{762}{625}{y}^3\right)⟦\frac{m}{s}⟧$

$\cdot 625$

$\left(7500x^3+2286y{x}^2-3048y^{2}x+762y^3\right)⟦\frac{m}{s}⟧$

$\mathrm{convert}\left(\,'\mathrm{units}'\,\frac{'\mathrm{mi}'}{'h'}\right)$

$\left(\frac{23437500}{1397}{x}^3+\frac{56250}{11}y{x}^2-\frac{75000}{11}{y}^{2}x+\frac{18750}{11}{y}^3\right)⟦\frac{\mathrm{mi}}{h}⟧$

$\mathrm{eval}\left(\,\left[x=3\mathrm{Unit}\left('s'\right)\,y=4\mathrm{Unit}\left('\min '\right)\right]\right)$

$10012333860⟦s^{2}m⟧$

$\mathrm{x2}≔t\mapsto \mathrm{x1}\left(t\right)+80.6\cdot \mathrm{Unit}\left(m\right)\:$

$\mathrm{diff}\left(\mathrm{x2}\left(t\right)\,t\right)$

$\frac{\ⅆ}{\ⅆt}\mathrm{x1}\left(t\right)$

The Units:-Simple subpackage was introduced in Maple 2017.

For more information on Maple 2017 changes, see Updates in Maple 2017.