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Screensize: 640 x 480 800 x 600 1024 x 768 1280 x 1024 UserName: Password: Anti-Spam Code: Format Mode: Basic  Help  Prompt  Format: Font Andale Mono Arial Arial Black Book Antiqua Century Gothic Comic Sans MS Courier New Georgia Impact Lucida Console Script MT Bold Stencil Tahoma Times New Roman Trebuchet MS Verdana   Size 1 2 3 4 5 6   Color Black Red Yellow Pink Green Orange Purple Blue Beige Brown Teal Navy Maroon LimeGreen Message: * HTML is OFF * Forum Code is ON Smilies [quote][i]Originally posted by thuang[/i] [br]hi, i just started learning origin (version 7.5) for the first time two days ago, and i need to do a whole sequence of modifications to fourier transformed data sets. i've been become familiar with origin's features but there's just some things i can't really figure out by myself so i'm looking for help in this forum. so i have some questions here, and sry if this is a really long post. and uh...one more thing is that i've never heard of fourier and his work until last week and i don't really understand it, but i i think i can get around that if i can smooth out these problems i have with understanding origin. so here goes: anyway, i have data sets from 2 epr absorbance spectra, one from a doubly spin labeled spectrum, and one from a singly spin labeled function. i integrate these two to get the normal obsorbance spectra, and i figured out that much with origin analysis > calculus > integrate. next i FFT both integrated spectra and i get a fft data set and a graph for each spectrum and i ran into my first problem. well, the next step is dividing one transformed spectrum into the other, getting a new transformed data set, and i'm not sure how to do that. i tried creating a new worksheet where the x variable was the frequency that is the same for both transformed spectra, and then i created a column for dividing the real parts of both spectra and another column to divide the imaginary parts of the spectra. but i'm not sure if this is how it's done. 1)so my first question is how exactly do i divide one transformed function into the other, to make a new function that is still a fourier transformed one. i'm guessing that this all has to do with math operations with the fft data columns but i'm not sure. after that i need to fit the real part of this new transformed function to a sum of two gaussians with an offset, and then subtract the offset. i read other posts where people have used multipeak fit, replicas, and user defined functions but i'm not sure which one is best for me. at the same time i think i need to keep the fit like a transformed function, because the next step is to reverse fourier transform the gaussian fit. 2) so the 2nd question is what is the best way to get a fit of the real part of the new transformed function as a sum of 2 gaussians and an offset? i get the impression that user defined is the most flexible way. 3)but then i don't know how to keep the function in a way that allows it to be reverse transformed. i think one of the posts and the manual said i may have to keep the imaginary part. but then how does that work if the fit is based on only the real part? and would the fit give me a new set of data? if it does then it would be simple to subtract the offset from the y column. after i have this untransformed fit, i need to multiply it by a constant and then integrate it from infinity to -infinity. 4) so would the final function i have after the reverse transform be in the form of a data set? then i can probably just set a new column as the final function times the constant and then integrate that? 5)and then i have one last question about the fft function: in the manual it warned that normalize and shift need to be unchecked in the fft window, or else the resulting functions would have problems when doing a reverse transform. i don't really know what this means, but i did try fft forward with and without shift and normalize and the results were different. but when i fft backwards with or without these 2, the real and imaginary were the same but then the Phi and the power were different. and i have no idea what those mean anyway. what should i do about shift and normalize? do you think it will affect my final calculations? whew, well that was a really long post. i hope i'm not taking too much of anyone's time with this. actually, i was thinking, origin seems to do EVERYTHING by performing operations on just data sets. or maybe i just know enough yet. wouldn't it be easier if all these steps could be done on functions in the form of equations? or maybe not? ok, that aaalllll the questions i have. so far. any help would be greatly appreciated, thanks. sry for being such a noob [/quote]   Check here to include your profile signature. Check here to subscribe to this topic.