| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

Last 100 entries

Sentidos Comunes (Chilean Online Magazine); Hilary Mantel: The Assassination of Margaret Thatcher - August 6th 1983; NSA Interceptng Gmail During Delivery; General IIR Filters; What's happening with Scala?; Interesting (But Largely Illegible) Typeface; Retiring Essentialism; Poorest in UK, Poorest in N Europe; I Want To Be A Redneck!; Reverse Racism; The Lost Art Of Nomography; IBM Data Center (Photo); Interesting Account Of Gamma Hack; The Most Interesting Audiophile In The World; How did the first world war actually end?; Ky - Restaurant Santiago; The Black Dork Lives!; The UN Requires Unaninmous Decisions; LPIR - Steganography in Practice; How I Am 6; Clear Explanation of Verizon / Level 3 / Netflix; Teenage Girls; Formalising NSA Attacks; Switching Brakes (Tektro Hydraulic); Naim NAP 100 (Power Amp); AKG 550 First Impressions; Facebook manipulates emotions (no really); Map Reduce "No Longer Used" At Google; Removing RAID metadata; New Bike (Good Bike Shop, Santiago Chile); Removing APE Tags in Linux; Compiling Python 3.0 With GCC 4.8; Maven is Amazing; Generating Docs from a GitHub Wiki; Modular Shelves; Bash Best Practices; Good Emergency Gasfiter (Santiago, Chile); Readings in Recent Architecture; Roger Casement; Integrated Information Theory (Or Not); Possibly undefined macro AC_ENABLE_SHARED; Update on Charges; Sunburst Visualisation; Spectral Embeddings (Distances -> Coordinates); Introduction to Causality; Filtering To Help Colour-Blindness; ASUS 1015E-DS02 Too; Ready Player One; Writing Clear, Fast Julia Code; List of LatAm Novels; Running (for women); Building a Jenkins Plugin and a Jar (for Command Line use); Headphone Test Recordings; Causal Consistency; The Quest for Randomness; Chat Wars; Real-life Financial Co Without ACID Database...; Flexible Muscle-Based Locomotion for Bipedal Creatures; SQL Performance Explained; The Little Manual of API Design; Multiple Word Sizes; CRC - Next Steps; FizzBuzz; Update on CRCs; Decent Links / Discussion Community; Automated Reasoning About LLVM Optimizations and Undefined Behavior; A Painless Guide To CRC Error Detection Algorithms; Tests in Julia; Dave Eggers: what's so funny about peace, love and Starship?; Cello - High Level C Programming; autoreconf needs tar; Will Self Goes To Heathrow; Top 5 BioInformatics Papers; Vasovagal Response; Good Food in Vina; Chilean Drug Criminals Use Subsitution Cipher; Adrenaline; Stiglitz on the Impact of Technology; Why Not; How I Am 5; Lenovo X240 OpenSuse 13.1; NSA and GCHQ - Psychological Trolls; Finite Fields in Julia (Defining Your Own Number Type); Julian Assange; Starting Qemu on OpenSuse; Noisy GAs/TMs; Venezuela; Reinstalling GRUB with EFI; Instructions For Disabling KDE Indexing; Evolving Speakers; Changing Salt Size in Simple Crypt 3.0.0; Logarithmic Map (Moved); More Info; Words Found in Voynich Manuscript; An Inventory Of 3D Space-Filling Curves; Foxes Using Magnetic Fields To Hunt; 5 Rounds RC5 No Rotation; JP Morgan and Madoff; Ori - Secure, Distributed File System; Physical Unclonable Functions (PUFs); Prejudice on Reddit

© 2006-2013 Andrew Cooke (site) / post authors (content).

FFT in scipy etc

From: andrew cooke <andrew@...>

Date: Thu, 4 Aug 2011 09:59:27 -0400

A quick example of generating an FTT using ipython / numpy / pylab etc.
Warning: I am not convinced this is correct.  My main reference is
http://www.scipy.org/scipy_Example_List#head-7b70c2c5bff1c7774581f834de2d11a995b4c988

Start ipython so that it will produce plots:

  > ipython -pylab
  Python 2.7 (r27:82500, Aug 07 2010, 16:54:59) [GCC]
  Type "copyright", "credits" or "license" for more information.

  IPython 0.10 -- An enhanced Interactive Python.
  ?         -> Introduction and overview of IPython's features.
  %quickref -> Quick reference.
  help      -> Python's own help system.
  object?   -> Details about 'object'. ?object also works, ?? prints more.

    Welcome to pylab, a matplotlib-based Python environment.
    For more information, type 'help(pylab)'.

  In [1]: # import what we need

  In [2]: from numpy import *

  In [3]: from pylab import *

  In [4]: # the data are a column of numbers that were sampled at 40Hz

  In [5]: y = genfromtxt('1312405054-23-result-KIV1-SHZ.txt')

  In [6]: len(y)
  Out[6]: 4000

  In [7]: # so generate an x axis

  In [8]: x=r_[0:100:1/40.0]

  In [9]: len(x)
  Out[9]: 4000

  In [10]: plot(x,y)
  Out[10]: [<matplotlib.lines.Line2D object at 0x1e46890>]

  In [11]: # now do the fft

  In [12]: s = fft(y)

  In [13]: plot(s)
  /usr/lib64/python2.7/site-packages/numpy/core/numeric.py:284: ComplexWarning: Casting complex values to real discards the imaginary part
    return array(a, dtype, copy=False, order=order)
  Out[13]: [<matplotlib.lines.Line2D object at 0x1dfc950>]

  In [14]: # that's the usual fft mess, so generate freq axis for half

  In [15]: f = 40*r_[0:2000]/4000.

  In [16]: plot(f,abs(s[0:2000])/4000)
  Out[16]: [<matplotlib.lines.Line2D object at 0x1e91090>]


Andrew

Comment on this post