beginner questions: return on Maxima console and working with implicit functions

2012/9/28 ivo welch <ivo.welch at anderson.ucla.edu>

> dear maxima experts---
>
> [1] I am trying to switch from Mathematica to Maxima.  I downloaded
> and installed it on ubuntu linux 12.04.1 .    I can use wxMaxima
> successfully.  I would like to use the basic command line interface.
> I type $ maxima, and then "solve( y + 2 == 0, y)" to the (%i1) prompt
> and hit enter...and nothing happens.  then I try shift-enter.  a ^c
> gets me a console interrupt.
>

Maxima needs a terminator at the end of an expression. Use ; to view the
answer and $ if the answer should not be displayd.

wxMaxima automatically adds a semicolon.

The operator for an equation is simply =


> [2] I am trying to work with implicit functions.  an illustration of
> what I want to accomplish is
>
> eqn : solve( y + log(y) + x = 0, y)
> plot(eqn, [x,0,1])
>

 To answer this I need to load an additional package:

(%i2) eqn : y + log(y) + x = 0$

(%i3) load(implicit_plot);

(%o3) "/usr/local/share/maxima/5.28.0/share/contrib/implicit_plot.lisp"
(%i4) implicit_plot(eqn, [x,0,1], [y,0,1])$


solve cannot solve eqn. So I load another package:

(%i5) load(to_poly_solve);

Loading maxima-grobner $Revision: 1.6 $ $Date: 2009-06-02 07:49:49 $
(%o5) "/usr/local/share/maxima/5.28.0/share/to_poly_solve/to_poly_solve.mac"
(%i6) to_poly_solve(eqn, y);

(%o6) %union([y = lambert_w(%e^-x)])
(%i7) plot2d(lambert_w(%e^-x), [x,0,1])$

To compute dy/dx I type

(%i8) diff(lambert_w(%e^-x), x);

(%o8) -%e^(-lambert_w(%e^-x)-x)/(lambert_w(%e^-x)+1)

I don't know much about Lambert's W function. So I can't help with dy/dx >
0.

I hope someone else can answer here.

Volker van Nek


> I know this is wrong...but how would I do this correctly?  (I also
> want to use M to ascertain whether dy/dx > 0 .)
>
> help for a poor beginner is appreciated.
>
> /iaw
>
>
> ----
> Ivo Welch (ivo.welch at gmail.com)
> http://www.ivo-welch.info/
> J. Fred Weston Professor of Finance
> Anderson School at UCLA, C519
> Editor, Critical Finance Review, http://www.critical-finance-review.org/
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