tag:blogger.com,1999:blog-3300702123878659843.post8594616694770585971..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Backward Linear PredictionGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-3300702123878659843.post-85221693592613204642020-01-08T09:35:24.303-05:002020-01-08T09:35:24.303-05:00Indralnil,
I have no expertise in computer code so...Indralnil,<br />I have no expertise in computer code so not in a position to offer any advice.<br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-73077823288312057042020-01-08T05:02:18.735-05:002020-01-08T05:02:18.735-05:00Hi Glenn,
The previous comment was just a hypothe...Hi Glenn,<br /><br />The previous comment was just a hypothetical situation. I am however looking for codes in C/C++/MATLAB that provides the predicted parameters and also does backward linear prediction if I give an FID (complex data vector) as input. I'd be grateful if you could provide with some sources of the same.Indranilnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-84572891173888454132019-11-07T10:27:32.258-05:002019-11-07T10:27:32.258-05:00Indranil,
Your question is clear. If you use back...Indranil,<br />Your question is clear. If you use backward linear prediction, both lines should ideally be in phase and require no correction if the pulse has zero width. If this is not the case, perhaps the dead time in your FID is not an exact multiple of the dwell time. In this case, the precision of the t=0 point would be quite low and the phases may not be correct. What is the frequency difference between the signals? <br /><br />Also see these posts....<br />https://u-of-o-nmr-facility.blogspot.com/2011/01/first-order-phase-errors.html<br />https://u-of-o-nmr-facility.blogspot.com/2015/04/dead-time-and-phase.html<br /><br />Glenn<br />Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-3919542681071275602019-11-07T10:03:01.815-05:002019-11-07T10:03:01.815-05:00Dear Glenn, thank you for your informative blog.
...Dear Glenn, thank you for your informative blog. <br /><br />Say I have exactly 2 frequencies in my FID of a one-pulse experiment. Now a dead time introduces first order phase problem (since the frequencies are different, they acquire different phases at the end of the dead time, and the amount of phase acquired is directly proportional to the magnitude of the frequencies).<br />Say the lower frequency component acquire a phase of 15 degrees and the higher frequency component acquire a phase of 35 degrees (Ideally their phases should be 0 if the signal was acquired from t=0). Now if I perform linear prediction then my predicted phase factors are 15 and 35 degrees respectively (and not 0 degrees for both components, which misleads me!). If I use this predicted parameters to back predict my FID then I'm essentially predicting wrongly, isn't it? <br />I hope I could make my question clear. How exactly does backward LP take care of the first order phase problem? Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-59693389945954721052009-03-27T04:36:00.000-04:002009-03-27T04:36:00.000-04:00Zhangzf,Thank you for the comment.1. Look at the ...Zhangzf,<BR/><BR/>Thank you for the comment.<BR/><BR/>1. Look at the beginning of the FID and decide how many points are "bad".<BR/>2. Throw away the bad points. You should throw away an even number of points otherwise your spectrum may be reversed on its frequency axis.<BR/>3. Do the backward linear prediction.<BR/>4. Fourier transform.<BR/><BR/>I hope this helps.<BR/><BR/>GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-10254680562256118152009-03-25T03:07:00.000-04:002009-03-25T03:07:00.000-04:00Dear Glenn,Shall I throw away the first portion of...Dear Glenn,<BR/>Shall I throw away the first portion of FID distorded before back LP?<BR/>1.I have done the back LP with an FID:first,I throw away the several points of the FID,and then do BLP,FT.I try 5 and 30 points,and the results confuse me:the spectrum with 5 points has more terrible phase than that of 30.Why?<BR/>2. In a spectrum with several peaks,after back LP,the smaller peaks seem to disapear.So what are the factors determining this?Zhangzfhttps://www.blogger.com/profile/15366049273829980907noreply@blogger.com