Mailman 3 August 2008 - SciPy-User

Is there a collection of useful functions/modules?
by Joshua 01 Aug '08

01 Aug '08

I'm very new to Python, as in only a week of programming, and was wondering if there is a page with a collection of highly useful functions/modules that are not necessarily maintained on a release-to-release basis for things like performing FFT's on data in a file. I wrote a function to do this using Numpy, and put in options to normalize the FFT for me, and take the absolute value. There are many other options I should add, but before I add complexity, I wouldn't mind having my code scrutinized, and made available for others to use and optimize. That way students and researchers don't have to reinvent the wheel, unless they want to or are using some odd formatting scheme. Just have the amplitude data in the list column wise. exempli gratia: 0.0 0.1 0.0 -0.1 ... et cetera. This code makes no particular frequency sampling assumptions (other than the sampling was done correctly), and only deals with simple FFT processing. I've attached the code and welcome scrutiny. There are few things that I know I should to add/restructure to my code: better error handling, printing out the phase, multi-dimensional analysis, and |Magnitude| in 20dB. Thanks for your help Joshua

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scipy.io.numpyio fwrite - appending or updating an array
by Brennan Williams 01 Aug '08

01 Aug '08

I have an existing binary file containing numpy array data. It has been created using open,fwrite & close and I can read the data using fread. I want to be able to either append a new array to the end of the file or update an existing array within the file. I've tried opening the file with a mode of either 'ab+' or 'wb+' and then writing the data using something like.... fd = open(vfname, 'ab+') if fd: filepos=(self.id-1)*self.yarray.size*4 fd.seek(filepos) fwrite(fd, self.yarray.size, self.yarray,'f') fd.close() When I use a mode of 'ab+' it looks like the data has been written to the file ok (no errors reported) but when I read it back I get my original data. When I use 'wb+' then my updated data gets written and read back ok. But when I reload the file, everything apart from my updated data (i.e. everything before it in the file) is now zero. The '+' in the mode seems to make no difference. What am I doing wrong? Thanks Bren.

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Numpy : in place moving data strange behaviour
by Samuel GARCIA 01 Aug '08

01 Aug '08

Hi list, I have a strange behaviour of numpy if I try to move in place a part of my array in an other place of the array. For 1D or for 2D there is not the same behaviour. The solution is of course copying the part I have move of thhe array. See the code : from scipy import * # for 1D a = arange(10) print a # a = [0 1 2 3 4 5 6 7 8 9] a[0:7] = a[3:10] print a # OK : a = [3 4 5 6 7 8 9 7 8 9] a = arange(10) print a a[3:10] = a[0:7] print a # OK a = [0 1 2 0 1 2 3 4 5 6] # for 2D a = concatenate( (arange(10)[newaxis,:] , arange(10)[newaxis,:]) ) print a #[[0 1 2 3 4 5 6 7 8 9] # [0 1 2 3 4 5 6 7 8 9]] a[:,0:7] = a[:,3:10] print a #OK a= # [[3 4 5 6 7 8 9 7 8 9] # [3 4 5 6 7 8 9 7 8 9]] a = concatenate( (arange(10)[newaxis,:] , arange(10)[newaxis,:]) ) print a a[:,3:10] = a[:,0:7] print a # Not expected a = #[[0 1 2 0 1 2 0 1 2 0] # [0 1 2 0 1 2 0 1 2 0]] # solution copy all the array : a = concatenate( (arange(10)[newaxis,:] , arange(10)[newaxis,:]) ) a[:,3:10] = a[:,0:7].copy() print a # OK a = #[[0 1 2 0 1 2 3 4 5 6] # [0 1 2 0 1 2 3 4 5 6]] Any explanation ? Thank Samuel -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Samuel Garcia Laboratoire de Neurosciences Sensorielles, Comportement, Cognition. CNRS - UMR5020 - Universite Claude Bernard LYON 1 Equipe logistique et technique 50, avenue Tony Garnier 69366 LYON Cedex 07 FRANCE Tél : 04 37 28 74 64 Fax : 04 37 28 76 01 http://olfac.univ-lyon1.fr/unite/equipe-07/ http://neuralensemble.org/trac/OpenElectrophy ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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