Home › Forums › Get Help › How do I ...? with Maple

A question about procedure

lemelinm's picture
Posted on 2008-07-20 06:30 By lemelinm (Maple Rating 3 227)
Categories:

Hi Everybody,

 

Suppose I have this procedure assign to p:

>p:=MyProc(args1,args2,args3,h) statement end proc:

where h is the step size.

args1 = {ode,ic} , args2 = x(t) et args3 = t=a..b.  The output of MyProc is a list of list

I would like to do what dsolve do when you write:

p:=dsolve( {ode,ic},x(t),x(t),numeric)

and then evaluate p(2) for example.

So my question is how can I make MyProc so I can evaluate p(2).  THis mean that p is a procedure given by the procedure MyProc.  I don't want to use global in my procedure.  Is this possible?

Mario

‹ Approx procedure bit level access to vector elements? ›
lemelinm's picture

An error in typo

Comment on 2008-07-20 06:32 from lemelinm (Maple Rating 3 227)

 The 6 th line should read:

p:=dsolve( {ode,ic},x(t),numeric)

sorry!

 

JacquesC's picture

I think what you want is

Comment on 2008-07-20 09:08 from JacquesC (Maple Rating 4 1699)

Your MyProc will look like

proc(args1, args2, args3, h)
    local v1, v2; # and more as needed

    statements; # these set things up
    proc(x) ssss end proc; # ssss uses v1, v2 and also args1, args2, etc
end proc;

This is how dsolve/numeric works.

lemelinm's picture

While we are on the subject

Comment on 2008-07-20 15:18 from lemelinm (Maple Rating 3 227)

<p>First of all, thanks you Jacques.&nbsp; Secondly, while on the subject of dsolve(...,numeric,..), I am wondering how Maple can give exactly, say, p(1/2) when the ics are x(a)=b.&nbsp; I know how to go from the ics to the left and from the ics to the right. </p>
<p>But, on the choice of h, nothing can assure me that I will be right on the spot (t=1/2).&nbsp; Does Maple redo the calculation with h = (a - 1/2)/N?&nbsp; This way, I am sure that the last calculation will be x(1/2)=something, wich is what I am looking for.</p>
<p><span><a href="http://www.mapleprimes.com/viewfile/2666"><img width="150" height="35" alt="" src="http://www.mapleprimes.com/scripts/image.php?image=http://www.mapleprimes.com/files/3867_Signature.jpg&amp;width=300&amp;height=300" /></a></span></p>

lemelinm's picture

Oups! sorry for the bad output

Comment on 2008-07-20 15:20 from lemelinm (Maple Rating 3 227)

 Let me retry again.

 

First of all, thanks you Jacques.&nbsp; Secondly, while on the subject of dsolve(...,numeric,..), I am wondering how Maple can give exactly, say, p(1/2) when the ics are x(a)=b. I know how to go from the ics to the left and from the ics to the right.

But, on the choice of h, nothing can assure me that I will be right on the spot (t=1/2). Does Maple redo the calculation with h = (a - 1/2)/N? This way, I am sure that the last calculation will be x(1/2)=something, wich is what I am looking for.
 

Robert Israel's picture

dsolve

Comment on 2008-07-20 17:05 from Robert Israel (Maple Rating 4 1460)

First of all, dsolve(..., numeric) isn't using a fixed step size, so your question doesn't quite make sense.  The default method is a Runge-Kutta-Fehlberg method.  But let's suppose you specified, say, method=classical[foreuler] for the Euler method which does have a fixed step size.  Now the actual numerical calculation doesn't happen until you call p(1/2), so the end point t=1/2 is known.  The step size can either be specified explicitly or chosen by Maple: if the latter, the choice is made by the procedure p itself.  Anyway, if 1/2-a is not an integer multiple of the step size, the last step will be made smaller so that it ends up at t=1/2.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
}