Tip 17. Units of nonphysical
values
Fig. 17.
Units of nonphysical values
See new picture too
In tip 15
we have considered the problem of linear programming about search of optimum
plan of issue of chairs. But we have not used the units even they have been
mentioned in the problem (see the table tip 15). In
the given problem both calculating units (chairs, people) and financial
units are used along with physical ones (meter, square meter and hour).
The
system variables  ïàêåò âñòðîåíû ñèñòåìíûå ïåðåìåííûå (see the sketch «Mathcad and
physical values» – http://twt.mpei.ac.ru/ochkov/Units/unit.htm)
are built-in in Mathcad, which keep units of physical values. But if you wish
you are able not only to introduce new units (see previous tip) but also new
values. The problem about plan of issue of chairs using units of all
values is solved in the fig. 17.
Unit
of American currency ($US) is introduced in the calculation
on the principle, as «Time is money»: physical value «time» is not used[1] in the given calculation and it is
possible to be «burdened» by the other function. Certainly it is simpler to
write: $US := 1 and thing := 1 (we have things are «attached» to
moles, which are not used in the calculation). But it is fraught with the
following mistake:
$US + thing = 2
Here the error message must appear:
«Incompatible dimensions» instead of numerical answer (two). In the
calculation, which you could see in the fig. 17,
physical and other values are introduced not only for more ôèçè÷åñêèå è
ïðî÷èå âåëè÷èíû ââåäåíû íå òîëüêî äëÿ
áîëüøåé «readability»
of the problem but also for additional control of compliance of dimensions in
the inputted formulas.