MaplePrimes - answers and comments on Question, Why does Maple do so badly at solving ODEs?

a common error: e is not exp(1)

Axel Vogt — Sat, 10 Dec 2011 00:52:46 Z

e is not exp(1), it is a symbol like a,b,c,d,e,f, ...

(D@@2)(y)(x)-D(y)(x)+2*y(x)=10*exp(-x)*sin(x); 
dsolve(%);

                       1/2                        1/2
                      7    x                     7    x
  y(x) = exp(x/2) sin(------) _C2 + exp(x/2) cos(------) _C1
                        2                          2

         + 5/3 (sin(x) + cos(x)) exp(-x)

exp

Markiyan Hirnyk — Sat, 10 Dec 2011 00:53:24 Z

Probably, you use e^(-x) instead of exp(-x). See ?exp .

Use exp

epostma — Sat, 10 Dec 2011 00:57:05 Z

Hi JerseyJohn,

It looks like you're using the regular variable e to represent the base of the natural logarithm. That doesn't work in Maple - it's just another variable. So Maple is solving a much more general differential equation.

You can use several different notations for specifying the base of the natural logarithm. The easiest one is often using the function ?exp. If I replace e^(-x) by exp(-x) in your input, I get the same answer that you show.

Hope this helps,

Erik Postma
Maplesoft.

?alias

gkokovidis — Sat, 10 Dec 2011 07:05:29 Z

See the help page for ?alias

Download exp_alias.mw

Regards,

Georgios Kokovidis

Dräger Medical

FAQ

pagan — Sat, 10 Dec 2011 02:03:37 Z

It's on Maplesoft's FAQ pages, here.

It's number 10 on Robert Israel's list of The Top 10 Maple Errors.

There is a room for Maple to improve, though.

No mention is made in that FAQ entry of the (obvious, to us) fact that 2D Math output displays exp(1) using the single character in another font (Roman, I guess, unlike regular variable names which display in italic). That's one reason why this problem comes up frequently; it's natural to try and input what you see as output. The font distinction is easy for a new user to miss.

That Maplesoft FAQ entry mentions that exp(1) can be inserted using the appropriate entry from the Expression Palette. But it doesn't point out that this is one way to get the typeset look or in 2D Math input mode. The typical new user and reader of that FAQ is unlikely to realize this.

Another possible improvement for that FAQ entry would be mentioning that command-completion can be used to promote exp(1) to in situ. (Actually, there is some goofiness to this,with the completion pop-up's left column showing exp_M , whatever that is supposed to mean, corresponding to the choice.)

Also, the 2D Math input parser/typestting mechanism doesn't automatically promote exp(1) to when it is typed normally. Why can't the GUI autopromote exp( similarly to how it handles sin ? Type in the letters s i n in 2D entry mode and the font switches. If the next letter is u then the font switches back. So why can't the typed characters e x p ( get autopromoted to the typeset with the cursor positioned in the superscript location? Sure, that might be aggresive and controversial, doing away with the need for command-completion. But why not go all the way with the wysiwig aspects?

It's not strictly true to say that Maple interprets e as just another name or variable. For 2D Math, that differs with font.

It's worth being fussy about detail, for a frequently asked question.

I suppose that's fair enough as an explanation.

JerseyJohn — Sat, 10 Dec 2011 02:53:53 Z

I suppose that's fair enough as an explanation. I'm trying to learn Maple in order to do more and better things than I can currently do in MathCAD (now there's a product which has stood still while Mathematica and Maple have forged ahead!)

Is there a way to assign the letter e to be the base of natural logarithms in Maple?