Error help: "Undefined value during function evaluation"

Error help: "Undefined value during function evaluation"

Post by Simon Li » Sun, 27 Jul 2003 19:31:18



Hi All,

I'm trying to use the "fit" function on some data that I collected in a
school experiment, but "fit" keeps on dying and giving the error "undefined
value during function evaluation". I am to fit data onto the following data:
20      78\n25  61\n30  45\n35  34\n40  24\n45  18\n50  13\n55  10
60      8\n65   6\n70   4\n75   3\n80   2
Using the function to be fitted as:
f(x) = a * exp(-1 * b * x) ; Where a, b are the constants fit is supposed to
give me

I am using gnuplot v. 3.7 patchlevel 1 on a WinXP box. After fit dies, I
used the command "show vars" to see what a and b during fitting and they
were:
pi = 3.14159265358979
a = 3.87069662567025e+40
b = 8.84029163816757e+42

Is fit dying because a and b are overflowing? How do I get a exponential
decay model out of my data set? I really need the values for my report, you
see.

I'm not a member of the mailing list, so send the suggestions to

Thanks in advance.

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Error help: "Undefined value during function evaluation"

Post by Hans-Bernhard Broeke » Mon, 28 Jul 2003 03:14:03



> I'm trying to use the "fit" function on some data that I collected in a
> school experiment, but "fit" keeps on dying and giving the error "undefined
> value during function evaluation". I am to fit data onto the following data:
> 20 78\n25  61\n30  45\n35  34\n40  24\n45  18\n50  13\n55  10
> 60 8\n65   6\n70   4\n75   3\n80   2

??? What are all those literal "\n" supposed to be doing in there?

Quote:> Using the function to be fitted as:
> f(x) = a * exp(-1 * b * x) ; Where a, b are the constants fit is supposed to
> give me

And what startup values did you give for a and b?

Quote:> I am using gnuplot v. 3.7 patchlevel 1 on a WinXP box. After fit dies, I
> used the command "show vars" to see what a and b during fitting and they
> were:
> pi = 3.14159265358979
> a = 3.87069662567025e+40
> b = 8.84029163816757e+42
> Is fit dying because a and b are overflowing?

More likely because exp(-b*x) is seriously underflowing.  Or because
due to the strange format of your data file, gnuplot only ever got to
see two datapoints, which is too few for a sensible two-parameter fit.

> I'm not a member of the mailing list, so send the suggestions to


No.  You write here -- you read here.

--

Even if all the snow were burnt, ashes would remain.

 
 
 

1. Help: "Activation Error: Error %1"

I'm currently sorting through a problem with the LW color selection button,
a problem that even the fine folk at Newtek tech support couldn't solve or
explain. Perhaps someone reading the postings can shed some light into my...
Wave.

My system:   Mac blue G3. 384 ram. System 8.5.1
My LW:       5.6d

The problem: When I select the "Surface Color" or "Light Color" button in
Layout I get a message that reads "Activation Error: Error %1." ...In
modeler the message is slightly different, but the result is the same; no
color selector. This only happens when the latest color plugin,
"gColorPicker.p", is loaded using either Config Update or the manual method.
When I re-enter the older plugin into the config file manually (I forget the
plugin name, "MacColor.p" or something) it works, but obviously without the
updated color selection options, just with the simple mac color wheel.

The particularly irritating thing about this "error" is that it came up from
nowhere, and now refuses to go away, even though by all accounts it
shouldn't even be there. Before it appeared the program ran about as solidly
as LW can on a mac, which is actually pretty stable, and with no apparent
glitches. Before it appeared nothing had changed in either LW or the system
that could explain it cropping up. I have played with the config files and
restarted with a base system and picked apart the system piece by piece and
reinstalled LW (a couple of times) called tech support and finally am
currently reinstalling my entire system from the ground up to try and find
the cause, but so far to no avail. Can anyone shed any light on this
problem?

Eternal gratefulness and showers of love will fall endlessly on anyone who
can help at all.

regards,
 Kent Matheson

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