Notes:
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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 and then enter the unit.
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When you edit a unit, double brackets appear around it.
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The default setting if none of the Units environments have been loaded is simple.
We can see this because combine/units accepts the following expression, which assumes the unassigned variable has a unit of length.
In either the Units/Standard or Units/Natural model, this expression is invalid. Notice that if we select the standard units mode, executing the same expression results in an error about adding , which is now implicitly unitless, and the term with a unit.
To verify that the correct mode was stored, we can call the UseMode command again.
With the currently selected mode, the default value for the symbolic option of the convert/units command is false. This means, for example, that Maple distinguishes between angles and unitless quantities, and between torque and energy; you cannot convert one to the other.
If we supply the option symbolic = true, or if we switch to the simple mode, then this conversion succeeds, with the implicit understanding that it is the energy required for applying the torque over an angle of one radian.
If we load the Units[Standard] package in a new Maple session to enable the Standard Units environment, the standard mode is automatically selected.
This means that the combine command we used above will throw an error, as before.
You can override the mode by calling UseMode again, or by explicitly supplying the mode option to the combine/units command. In either case, you need to be careful, otherwise the addition operator, +, generates an error before it gets to combine/units. This can be overcome by explicitly using the top level version of + instead of the one from the Units[Standard] package.
Loading the Units package also loads one of the Units subpackages, as indicated by the currently selected mode. By default, this is the Units[Simple] subpackage, but this can be overridden using the UseMode command.
Automatically loading the Units[Simple] subpackage
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Automatically loading the Units[Standard] subpackage
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