Plotting procedure solutions

Posted on 2008-02-13 09:51 By Wayne (

57)

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How do I ...? with Maple

A procedure named curve(x) in the attached worksheet solves several equations, each dependent on the solution to the previous equation. The problem is that when I issue the plot command for a range of the dependent variable x, the equation result that gets plotted is not for the result of the solution to the last equation for P. Specifically, I would like to issue the "plot(curve,0.0..0.5, <other format commands>);" and get a plot of k vs. P. Currently the plot is of k vs. P_bar. Your comments are appreciated.

View 4865_Procedure Results.mw on MapleNet or Download 4865_Procedure Results.mw
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Are you sure?

Comment on 2008-02-13 10:49 from Doug Meade ( Maple Rating 4

721)

Why do you believe the plot is of k vs. P_bar?

If, in the definition of curve, you remove the definition of P, the plot is different. Create a copy of curve, say curve2, but remove the definition of P_bar. Then, plot both curve and curve2. Here's the command I used:

plot([curve, curve2], 0. .. .5, view = [0 .. .1, 0 .. 9000],
  axes = boxed, gridlines = true, title = "P - k RELATION",
  labels = ["k", "P"]);

The shapes are similar, but the plotted points are clearly different.

Am I missing something?

Doug

---------------------------------------------------------------------
Douglas B. Meade
Math, USC, Columbia, SC 29208  E-mail: mailto:meade@math.sc.edu       
Phone:  (803) 777-6183         URL:    http://www.math.sc.edu/~meade/

Mea culpa, however...

Comment on 2008-02-13 12:43 from Wayne (

57)

Doug,

You are exactly right, I was not reading the plotted results correctly; however, assuming I did want to plot (or otherwise use the value of P_bar in an expression), does the fact that I have declared it as a global variable mean that it retains it's value outside of the procedure?

Thank you for your comments (and patience).

Wayne J. Bell AREVA NP, Inc. Charlotte, North Carolina

P and P_bar

Comment on 2008-02-13 21:00 from Robert Israel ( Maple Rating 4

1460)

The result returned by a procedure is the result of the last statement it executes.

In your case the procedure curve returns the value of P because that's the last thing it calculates. As a side effect it also assigns values to the global variables P_bar and P. But of course those values will be overwritten the next time curve is called.