Thorsten, I'd suggest you use multiplication (*) instead of the "`"
operator throughout your calculation (e.g. 2*m instead of 2`m). At the
very end, you can substitute e.g. psubst([1 ` m = m, 1 ` kg = kg, ...],
...) and then use whatever facilities are useful from the ezunits package.
I don't think the ezunits convention works very well with the rest of
Maxima in general; the handling of units should probably be rethought.
-s
On Wed, Oct 31, 2012 at 12:22 AM, Robert Dodier <robert.dodier at gmail.com>wrote:
> On 2012-10-29, Thorsten Bonow <thorsten.bonow at withouthat.org> wrote:
>
> > I'm trying to use "ezunits" to do some calculations, but when using
> units,
> > "solve" looses its capability of solving even simple equations.
>
> 'solve' doesn't know anything about units, so from its point of view,
> an expression with units is treated the same as some random function or
> operator. Some such expressions can be solved by 'solve', some can't.
>
> 'solve' can solve variants of the problem you posed if "`" is replaced
> by a function or operator. I haven't figured out why it can't solve the
> original. In the interest of getting to a solution, my advice is to
> solve it symbolically first, then substitute specific values into the
> solution:
>
> solve ([A = a*b, b = c*d], [A, b]);
> => [[A = a*c*d,b = c*d]]
> subst ([a = 1`m, c = 2`m, d = 3`m], %);
> => [[A = 6 ` m^3,b = 6 ` m^2]]
>
> > Is ezunits mainly for unit conversion or is there a way for
> > calculating with units?
>
> I don't know what you have in mind, but ezunits is supposed to be a way
> to handle units symbolically. So if you have some such problems to
> solve, I would be interested to hear about it. Take a look at the
> examples shown by demo(ezunits), especially the one about the speed of
> sound toward the end.
>
> best
>
> Robert Dodier
>
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