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learning how to use mpfit,. need help [message #87740]

Tue, 25 February 2014 13:35

alkyl47
Messages: 2
Registered: February 2014

Junior Member

Hi

I am new to idl and learning how to use mpfit but run into error, please help if you have time.

IDL version 6.3

////////////////////
IDL> x = findgen(101)
IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)
% Program caused arithmetic error: Floating underflow
///////////////////

these are the tutorial from the daedalus.as.arizona.edu group.

thanks in advance.

LR

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Re: learning how to use mpfit,. need help [message #87741 is a reply to message #87740]

Tue, 25 February 2014 13:44

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

alkyl47@gmail.com writes:

> I am new to idl and learning how to use mpfit but run into error, please help if you have time.
>
>
> IDL version 6.3
>
> ////////////////////
> IDL> x = findgen(101)
> IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)
> % Program caused arithmetic error: Floating underflow
> ///////////////////
>
> these are the tutorial from the daedalus.as.arizona.edu group.

Can't help you with MPFIT because I can't even see where you are using
it. I can help with underflow errors, the nemesis of many an IDL
programmer:

http://www.idlcoyote.com/math_tips/underflow.html
http://www.idlcoyote.com/code_tips/underflow.html

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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Re: learning how to use mpfit,. need help [message #87742 is a reply to message #87740]

Tue, 25 February 2014 13:55

alkyl47
Messages: 2
Registered: February 2014

Junior Member

On Tuesday, February 25, 2014 11:35:53 AM UTC-10, alk...@gmail.com wrote:
> Hi
>
>
>
> I am new to idl and learning how to use mpfit but run into error, please help if you have time.
>
>
>
>
>
> IDL version 6.3
>
>
>
> ////////////////////
>
> IDL> x = findgen(101)
>
> IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)
>
> % Program caused arithmetic error: Floating underflow
>
> ///////////////////
>
>
>
> these are the tutorial from the daedalus.as.arizona.edu group.
>
>
>
> thanks in advance.
>
>
>
> LR

Yes, I am slowly getting to mpfit but in order to learn the usage, I need to generate noisy gaussian curve per this web site but did not get very far.

http://daedalus.as.arizona.edu/wiki/mpfit

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Re: learning how to use mpfit,. need help [message #87746 is a reply to message #87740]

Tue, 25 February 2014 15:42

Harald Frey
Messages: 41
Registered: March 1997

Member

On Tuesday, February 25, 2014 1:35:53 PM UTC-8, alk...@gmail.com wrote:
> Hi
>
>
>
> I am new to idl and learning how to use mpfit but run into error, please help if you have time.
>
>
>
>
>
> IDL version 6.3
>
>
>
> ////////////////////
>
> IDL> x = findgen(101)
>
> IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)
>
> % Program caused arithmetic error: Floating underflow
>
> ///////////////////
>
>
>
> these are the tutorial from the daedalus.as.arizona.edu group.
>
>
>
> thanks in advance.
>
>
>
> LR

Do this in double precision and you will not get the error:

IDL> x = dindgen(101)
IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)

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Re: learning how to use mpfit,. need help [message #87748 is a reply to message #87740]

Tue, 25 February 2014 20:13

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Tuesday, February 25, 2014 4:35:53 PM UTC-5, alk...@gmail.com wrote:
> IDL> y = 25.*exp(-(x-32.)^2/(2*5.^2))+2.*randomn(0,101)
> % Program caused arithmetic error: Floating underflow

Floating underflow is almost never an error. It's just warning you that exp(-large_number) far from the centroid of the gaussian, has truncated precision or is being set to zero. Plot your data and you will see it's fine.

Craig

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