Why don't I get a float result?

Question

c2: (x-0.5)^2+y^2=1;
solve(c2,y);
cs2: map(rhs, %);
at(cs2,[x=0.5]);

I expect to see [-1,1], but I get this instead

What should I do?

Incidentally, maxima cannot plot this equation for a reason unknown to me.

plot2d(cs2, [x,-2.5,2.5],[same_xy, true]);

plot2d: expression evaluates to non-numeric value everywhere in plotting range.
plot2d: expression evaluates to non-numeric value everywhere in plotting range.
plot2d: nothing to plot.

Build info:

wxbuild_info();
wxMaxima version: 19.07.0
using wxWidgets version: wxWidgets 3.0.4
Maxima version: 5.43.2
Maxima build date: 2020-02-21 05:22:38
Host type: x86_64-pc-linux-gnu
System type: BSD BSD NIL
Lisp implementation type: GNU Common Lisp (GCL)
Lisp implementation version: GCL 2.6.12

Whole output:

Try writing the exponents as `c2: (x - 0.5)^2 + y^2 = 1`, i.e., with a caret and numeral 2 instead of superscript 2. It might help shed some light to write `solve(c2, y); cs2: map(rhs, %);` so you can see the result of `solve` before going on. If it's still not working, my advice is to update this post with all the inputs and outputs. By the way, what does `wxbuild_info()` report? — Robert Dodier, Jan 30 '22 at 18:58

score 0 · Accepted Answer · answered Jan 31 '22 at 20:27

I can't reproduce the behavior you're seeing. I compiled Maxima 5.43.2 (version number slightly mixed up in build_info output below) and I don't get the results you're seeing. Here's what I see with the command line interface (I get the same result with wxMaxima).

(%i1) c2: (x - 0.5)^2 + y^2 = 1;
                               2            2
(%o1)                         y  + (x - 0.5)  = 1
(%i2) solve (c2, y);

rat: replaced -0.5 by -1/2 = -0.5
                          2                             2
               sqrt((- 4 x ) + 4 x + 3)      sqrt((- 4 x ) + 4 x + 3)
(%o2)   [y = - ------------------------, y = ------------------------]
                          2                             2
(%i3) cs2: map (rhs, %);
                          2                         2
               sqrt((- 4 x ) + 4 x + 3)  sqrt((- 4 x ) + 4 x + 3)
(%o3)       [- ------------------------, ------------------------]
                          2                         2
(%i4) at (cs2, x = 0.5);
(%o4)                            [- 1.0, 1.0]
(%i5) plot2d(cs2, [x,-2.5,2.5],[same_xy, true]);
plot2d: expression evaluates to non-numeric value somewhere in plotting range.
plot2d: expression evaluates to non-numeric value somewhere in plotting range.
(%o5)             [/tmp/maxout9196.gnuplot, /tmp/maxplot.x11]

The plot2d displays a circle.

For the record, build_info reports:

Maxima version: "5.43.1_10_g5476356eb"
Maxima build date: "2022-01-31 12:13:20"
Host type: "i686-pc-linux-gnu"
Lisp implementation type: "CLISP"
Lisp implementation version: "2.49 (2010-07-07) (built 3605610186) (memory 3852648802)"
User dir: "/home/robert/.maxima"
Temp dir: "/tmp"
Object dir: "/home/robert/tmp/maxima-read-only-git/maxima-code/binary/5_43_1_10_g5476356eb/clisp/2_49__2010_07_07___built_3605610186___memory_3852648802_"
Frontend: false

It's puzzling that you are seeing a different result for solve. Do you get the same result in command line Maxima, or something else?

Why don't I get a float result?

1 Answers1