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Unused x-values in derivative w/ curve.x & sgderiv

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[quote][i]Originally posted by JSchoeck[/i]
[br]Hi all,

I'm trying to calculate the derivative of a dataset that has varying and non-uniform x-value distances.

According to all examples I've found in the help and this forum the appropriate parameter to set the column for the x-values is "curve.x$ = wks_X;". Sadly, Origin ignores the x-values and assumes a uniform distance on the x-axis of 1.

Here's the command I'm using:

[code]curve.x$ = wks_U;
curve.data$ = wks_I;
curve.result$ = wks_Deri;
curve.i1 = -1;
curve.smoothpts = 5;
curve.derivdeg = 1;
worksheet -t 2 4; //the 2nd column is I and originally type Y
curve.sgderiv();
worksheet -t 2 1; //converting it back to a Y-axis for plotting purposes
[/code]

A problem that I have is that the derivative is only then calculated as long a the data-column is of the X-type (even though it should be of the Y-type!). That's why I declared it to be X-type initially, but of course this cannot be correct.

Can anyone point out the correct way of using a X-value column and a Y-value column together with curve.sgderiv() please?

Thanks for your time,
Johannes

Origin Ver. and SR (Select Help-->About Origin): 8 SR4
Operating System: WinXP
[/quote]

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T O P I C R E V I E W
JSchoeck	Posted - 01/09/2009 : 04:57:18 AM Hi all, I'm trying to calculate the derivative of a dataset that has varying and non-uniform x-value distances. According to all examples I've found in the help and this forum the appropriate parameter to set the column for the x-values is "curve.x$ = wks_X;". Sadly, Origin ignores the x-values and assumes a uniform distance on the x-axis of 1. Here's the command I'm using: curve.x$ = wks_U; curve.data$ = wks_I; curve.result$ = wks_Deri; curve.i1 = -1; curve.smoothpts = 5; curve.derivdeg = 1; worksheet -t 2 4; //the 2nd column is I and originally type Y curve.sgderiv(); worksheet -t 2 1; //converting it back to a Y-axis for plotting purposes A problem that I have is that the derivative is only then calculated as long a the data-column is of the X-type (even though it should be of the Y-type!). That's why I declared it to be X-type initially, but of course this cannot be correct. Can anyone point out the correct way of using a X-value column and a Y-value column together with curve.sgderiv() please? Thanks for your time, Johannes Origin Ver. and SR (Select Help-->About Origin): 8 SR4 Operating System: WinXP
3 L A T E S T R E P L I E S (Newest First)
VincentLiu	Posted - 01/12/2009 : 04:49:10 AM quote: Originally posted by JSchoeck Thanks for the hint. :) You can also select Analysis-> Mathematics-> Differentiate open the Differentiate dialog to get the derivative of a dataset. For more details please refer to http://www.originlab.com/www/helponline/Origin8/en/mathematics/differentiate.htm
JSchoeck	Posted - 01/12/2009 : 04:24:18 AM Thanks for the hint. :)
VincentLiu	Posted - 01/12/2009 : 04:02:29 AM curve.sgderiv() uses Savitzky-Golay method to differentiate the dataset. And the Savitzky-Golay method requires a constant X-spacing within the data. So that why you cannot get the right results. Origin offers another function "Derivative" to calculate the derivative, which do not need a constant X-spacing within the data. For more details, please first select Help-> Programming-> LabTalk to open the LabTalk CHM. Then choose Search tab to search with the keywords Derivative. Best regard, Vincent OriginLab Tech Services

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