[Maxima-bugs] [ maxima-Bugs-1605201 ] wronskian documentation

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Bugs item #1605201, was opened at 2006-11-29 06:06
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Category: Documentation
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: wronskian documentation

Initial Comment:
(1) Either wronskian needs to auotload, or the user
documentation needs to say that to use the wronskian
function you must load functs.

(2) The last sentence of the user documentation is
wrong: "The functions are linearly dependent if this 
determinant is zero." The standard counterexample
is x -> x |x| and  x -> x^2. On the reals, these 
functions are linearly independent, yet the
determinant of their wronskian matrix vanishes.

(3) The claim that "<f_1>, ..., <f_n> may be the names 
of user-defined functions, or.." is either wrong or
misleading. Things like

(%i41) f(x) := x^2$
(%i42) g(x) := x^3$
(%i43) wronskian([f,g],x); 

do not work.

(4) Final non-documentation comment: If a Maxima
function signals an error, if at all possible, the
error should come from the calling function, not
some other function. Thus I don't like:

(%i45) wronskian(1+x,x);
Invalid matrix row:x+1

If the first argument isn't a list, wronskian should
either return a noun form, or signal an error such
as "The first argument to wronskian must be a list."
When the error comes from matrix, the user doesn't
really know what went wrong or how to fix it.

Barton


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