Larry Evans <cppljevans at suddenlink.net> writes:
> The following wxmaxima session:
>
> (%i7) InMoney: 55*long+1.06*short=5;
> (%o7) 1.06*short+55*long=5
> (%i8) outMoney: 48.5*long+1.06*short=0;
> (%o8) 1.06*short+48.5*long=0
> (%i9) linsolve([InMoney,OutMoney],[long,short]);
> rat: replaced 1.06 by 53/50 = 1.06
> (%o9) []
>
> give the wrong answeer.
I tried out your code and found the mistake. Here's my transcript:
Maxima branch_5_30_base_132_gd543604 http://maxima.sourceforge.net
using Lisp SBCL 1.0.57.0.debian
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) InMoney: 55*long+1.06*short=5;
(%o1) 1.06 short + 55 long = 5
(%i2) outMoney: 48.5*long+1.06*short=0;
(%o2) 1.06 short + 48.5 long = 0
(%i3) solve([InMoney,OutMoney]);
solve: more unknowns than equations.
Unknowns given :
[OutMoney, short, long]
Equations given:
[1.06 short + 55 long = 5, OutMoney]
-- an error. To debug this try: debugmode(true);
Hmm. Weird. But look carefully: OutMoney is not the same thing as
outMoney (the former is an unknown variable; the latter is an equation
you defined). Fixing the case:
(%i4) solve([InMoney,outMoney]);
rat: replaced 1.06 by 53/50 = 1.06
rat: replaced 48.5 by 97/2 = 48.5
rat: replaced 1.06 by 53/50 = 1.06
24250 10
(%o4) [[short = - -----, long = --]]
689 13
Or, calling linsolve():
(%i5) linsolve([InMoney,outMoney], [long, short]);
rat: replaced 1.06 by 53/50 = 1.06
rat: replaced 48.5 by 97/2 = 48.5
rat: replaced 1.06 by 53/50 = 1.06
10 24250
(%o5) [long = --, short = - -----]
13 689
(%i6) float(%);
(%o6) [long = .7692307692307693, short = - 35.19593613933237]
Here, linsolve() is rather less helpful when given confusing inputs than
solve() is. I suppose it's not really a bug: an overdetermined set of
linear equations just doesn't have any nonzero solutions, so returning
an empty list is the right thing to do.
Rupert
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