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Re: Radon forward projection problem [message #60142 is a reply to message #60021]

Mon, 28 April 2008 06:33

mmiller3
Messages: 81
Registered: January 2002

Member

>>>> > "Wox" == Wox <nomail@hotmail.com> writes:

> Ah, so I'm using MLEM :-). However, my initial problem
> still stands. What should one do when FP(v) is zero in
> some pixels, that is in formula

> v'=v * BP(s0/FP(v))/BP(s1)

This is a common problem in numerical codes. When dividing, I
usually pick a small threshold value, epsilon, and ensure that my
value is greater than epsilon before dividing:

IDL> x=findgen(50)
IDL> y = x
IDL> epsilon = 10
IDL> y[where(x le epsilon)] = epsilon
IDL> plot, 1/x
% Program caused arithmetic error: Floating divide by 0
IDL> plot, 1/y

Or something along those lines.

Mike

--
Michael A. Miller mmiller3@iupui.edu
Imaging Sciences, Department of Radiology, IU School of Medicine

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[Message index]

		Radon forward projection problem By: Wox on Tue, 22 April 2008 08:07
		Re: Radon forward projection problem By: Wox on Thu, 24 April 2008 04:14
		Re: Radon forward projection problem By: mmiller3 on Thu, 24 April 2008 09:22
		Re: Radon forward projection problem By: mmiller3 on Wed, 23 April 2008 09:53
		Re: Radon forward projection problem By: Vontobel Peter on Wed, 23 April 2008 03:42
		Re: Radon forward projection problem By: Wox on Wed, 23 April 2008 03:02
		Re: Radon forward projection problem By: Vontobel Peter on Wed, 23 April 2008 00:42
		Re: Radon forward projection problem By: Wox on Sun, 27 April 2008 04:16
		Re: Radon forward projection problem By: mmiller3 on Mon, 28 April 2008 06:33

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