**To**:**Ansley Manke <ansley.b.manke@xxxxxxxx>****Subject**:**Re: [ferret_users] correlation coefficient using variance.jnl****From**:**Ms Sindu Raj Parampil <parampil@xxxxxxxxxxxxxxxxxx>**- Date: Fri, 18 Sep 2009 13:13:14 +0530 (IST)
- Cc: oar.pmel.ferret_users@xxxxxxxx
- In-reply-to: <4AB2608D.3050000@xxxxxxxx>
- References: <Pine.LNX.4.58.0909171203410.4248@xxxxxxxxxxxxxxxxxx> <4AB2608D.3050000@xxxxxxxx>
- Sender: owner-ferret_users@xxxxxxxx

Hello Ansley, Thank you for the suggestion. I listed the different variables used in calculation of correlation from both cases. Variance.jnl calculates CORREL= COVAR / (P_VAR_MASK*Q_VAR_MASK)^.5 For case 1 (i.e., p = isoairs, q = isorama and correl = 0.2269), COVAR = 0.4739, P_VAR_MASK = 1.506, Q_VAR_MASK = 2.897 For case 2 (i.e., p = isorama, q = isoairs and correl = undefined), COVAR = 0.4551, P_VAR_MASK = 2.931, Q_VAR_MASK = 1.504 So case 2 does have values upto the penultimate step. Yet, its not calculating the correlation. When these values are manually plugged in the expression, CORREL= COVAR / (P_VAR_MASK*Q_VAR_MASK)^.5 the CORREL = 0.2168. This is still different from CORREL case 1 (0.2269). Meanwhile a friend mentioned that the different grids of variables (isoairs, isorama) could be reasponsible for the different CORRELs. So I wrote the variables out into a text file and read them onto the same grid. This solved the problem and now both CORRELs match! thanks and regards Sindu On Thu, 17 Sep 2009, Ansley Manke wrote: > Hi Sindu, > Yes, the correlation should be the same when p and q are reversed, and a > simple test I just tried does result in the same correl regardless of > which variable is P and which is Q. Something odd seems to be happening > with your data. > > One thing to try is after the first command > > let p = isorama[k=1]; let q = isoairs[k=1]; go variance ; li correl > > then do "cancel variable/all; cancel memory", before > > let p = isoairs[k=1]; let q = isorama[k=1]; go variance ; li correl > > which will make sure that the data is read again and everything is > reinitialized. I don't really know that this will make any difference. > > If the result of the second definitions is still missing, to try to find > out what might be going on, you could look at the variables that are > defined by the variance.jnl script: > > yes? go variance > yes? go/help variance ! lists the commands in the script > > Then just list or plot the values of the different variables that are > defined as the script builds up the definition of correl. For instance > > list p_ave, q_ave > list p_dev, q_dev ! or plot p_dev, q_dev > > and so forth. This may show that one variable has lots of missing data, > perhaps, or some other peculiar behavior that's causing this. > > Please write back and let us know what you find out. > > > Ansley > > > Ms Sindu Raj Parampil wrote: > > Hello, > > I've encountered a problem while calculating correlation using the > > 'variance.jnl' between 2 variables: isorama and ISOAIRS. > > > > When I choose p = isorama & q = isoairs to run variance.jnl, the > > correlation coefficient is 0.2269. But when p and q are reversed > > (i.e., p = isoairs & q = isorama ), the correlation is undefined. > > > > Shouldn't the corr. coeffs be same irrespective of the order of the > > variables for simultanoeus correlation? > > > > Pls see below for the commands I used in both cases and the ferret > > calculations. > > 1) let p = isorama[k=1]; let q = isoairs[k=1]; go variance ; li correl > > > > VARIABLE : CORRELATION OF P AND Q > > FILENAME : RH_1s90e_03_04.nc > > LONGITUDE: 90E > > LATITUDE : 1.5S > > DEPTH (m): -3 > > TIME : 31-DEC-2002 12:00 to 08-JUN-2004 12:00 > > 0.2269 > > > > 2) let p = isoairs[k=1]; let q = isorama[k=1]; go variance ; li correl > > > > VARIABLE : CORRELATION OF P AND Q > > FILENAME : RH_1s90e_03_04.nc > > LONGITUDE: 89.5E > > LATITUDE : 1.5S > > HEIGHT (millibar): 1000 > > TIME : 31-DEC-2002 12:00 to 08-JUN-2004 12:00 > > .... > > > > I use FERRET v6.2 on OpenSuse 11.0. Any help is appreciated. > > Thank you > > Sindu > > > > > > -- Sindu Raj Parampil Ph.D Student Centre for Atmospheric and Oceanic Sciences Indian Institute of Science Bangalore ======================================================================= "Knowledge of the oceans is no longer a matter of curiosity; our very survival may hinge upon it" John F. Kennedy ======================================================================= -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.

**Follow-Ups**:**Re: [ferret_users] correlation coefficient using variance.jnl***From:*Ansley Manke

**References**:**[ferret_users] correlation coefficient using variance.jnl***From:*Ms Sindu Raj Parampil

**Re: [ferret_users] correlation coefficient using variance.jnl***From:*Ansley Manke

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