Re: Eigenvalue problem in mathematica...

*To*: mathgroup at smc.vnet.net*Subject*: [mg93767] Re: Eigenvalue problem in mathematica...*From*: "sjoerd.c.devries at gmail.com" <sjoerd.c.devries at gmail.com>*Date*: Tue, 25 Nov 2008 07:17:45 -0500 (EST)*References*: <gg62l4$537$1@smc.vnet.net>

Bulash, I can see several problems here: First, what is this ODE package? As far as I know, differential equations are done in Mathematica using DSolve or NDsolve. Are you sure you're not using a another system's package or so (they end in .m as well)? Anyways, I don't see a statement in your program in which you load this package (Needs[ ] or <<), so don't expect Mathematica to know the ODE function automatically. And then there is the use of the set delayed construction ( := ) for all of your assignments, even involving constants. For constants, := is never essential or useful and Set ( = ) usually yields a much faster program. The difference between the two is that in an assignment like a=b+5 the right-hand side is evaluated immediately and the result is used whenever the righthand side is used. The value of b at the time of the assignment to a is used. In a:=b+5 the right-hand side is *not* evaluated until a is actually used in an evaluation. The value of b at that time is used, *not* the value at the time of the assignment to a. Your definition of p ("p[r_] := e^Integrate[B[r]/A[r], r]") has several problems: I assume you want e to be the exponential constant. That should be either entered as E or esc-ee-esc in Mathematica. The integral itself is a very complicated function and will take for ages to solve (if a solution can be found at all, of which I'm not sure). Due to the ':=' it is calculated *every* time p[r] is used. Furthermore, if you would like to evaluate p[5] this would yield e^Integrate[B[5]/A[5], 5] which is clearly nonsense (no integration variable left here). You should really use '=' here. Or perhaps you meant something like: p[r_] := E^Integrate[B[r1]/A[r1], {r1,0,r}] ? Cheers -- Sjoerd

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