Mailman 3 August 2006 - SciPy-User

Re: [SciPy-user] hough transform again
by stephen emslie Aug. 24, 2006

Aug. 24, 2006

It could be that Stefan's hough is fast because it uses only one for loop, and lots of array operations, which I believe are fast. Speed is definitely going to be an issue for me, as I'm going to need to be able to process a video feed in real-time. But I'd like to try and get things working with scipy and radon to start, and then look at speeding things up. Thanks for the link. btw, hope you dont mind if I send this to the list too. Perhaps someone will be able to give some more insight into hough, radon, inverse radon, speed, etc. Stephen On 8/22/06, Brent Pedersen <bpederse(a)gmail.com> wrote: > > hi again, this page makes the inverse radon seem fairly do-able: > http://www.owlnet.rice.edu/~elec431/projects96/DSP/bpanalysis.html<http://www.owlnet.rice.edu/%7Eelec431/projects96/DSP/bpanalysis.html> > i'm going to try to implement. > at least all the tools are in sci/num-py, just have to put them > together... > i still wonder why the stefan's hough is so much faster than scipy's > radon, i guess the imrotate in radon must be pretty expensive. > > -b > > > On 8/22/06, stephen emslie <stephenemslie(a)gmail.com> wrote: > > > > > > also, have you seen radon() in scipy.misc ? > > > if only there was an inverse_radon(). > > > > > > > > > I'm taking a look at it now. The Radeon transform looks like it might be > > more effective than the Hough transform. Even so, I think it would be nice > > to have a Hough transform in scipy. Of course there's still that problem of > > the inverse transform as you say. It would definitely be handy to have! > > > > Stephen > > > > >

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odr weighted residuals
by Christian Kristukat Aug. 24, 2006

Aug. 24, 2006

Hi, this is probably a question for Robert but other people might be interested in this as well, so here it goes: Does odr support weighted residuals such that data points which are far away from the bulk of points have small weights? I could think of doing that externally by running odr once, looking at the residuals, calculating new weigths and restarting the fit but of course I'd prefer to not to do it like this. Regards, Christian

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weave: C-float argument does not accept python int value
by Sebastian Haase Aug. 23, 2006

Aug. 23, 2006

Hi, I'm really excited about weave - it's great fun ! Now I get this error message: Conversion Error:, received 'int' type instead of 'float' for variable 'pz' Apparently if I call my functions "f" like f(5) but f was defined in C as: void f(double pz) I get that error. Did I understand this correct ? And how could I specify a "converter" so that a int gets "automagically" converted into a float !? Thanks for weave, Sebastian Haase

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find roots for spherical bessel functions...
by fred Aug. 22, 2006

Aug. 22, 2006

Hi all, I'm trying to find out the first n roots of the first m spherical bessel functions Jn(r) (and for the derivative of (r*Jn(r))), for 1<m,n<100. So, I decided to use optimize func, such as fsolve() or brentq(). My problem is to find out x0, the "seed" to start to find the root, for fsolve(), or the bounds [a,b] for brentq(). I tried x0 = alpha + beta*n, where alpha \approx 3.5 & beta \approx 1, but there is always an order for which it fails : for brentq(), you must have f(a)*f(b) < 0. Is there anyone who has any idea to estimate x0 or [a,b] for the nth root of the mth spherical Bessel function (same question for (rJn(r))') Here's my code. def Jn(r,n): return (sqrt(pi/(2*r))*jv(n+0.5,r)) def Jn_zeros(n,nt): r0 = 3.5 + n val = zeros(nt) i = 0 while (i < nt): foo = brentq(Jn, r0, r0+pi, (n,)) val[i] = foo i = i + 1 r0 = foo + pi return (val) def rJnp(r,n): return (0.5*sqrt(pi/(2*r))*jv(n+0.5,r) + sqrt(pi*r/2)*jvp(n+0.5,r)) def rJnp_zeros(n,nt): r0 = 3.5 + n - pi/2 val = zeros(nt) i = 0 while (i < nt): foo = brentq(rJnp, r0, r0+pi, (n,)) val[i] = foo i = i + 1 r0 = foo + pi return (val) Thanks in advance. Cheers, -- Fred.

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spherical harmonic
by fred Aug. 22, 2006

Aug. 22, 2006

Hi, I'm playing with spherical harmonic (special.sph_harm()) and I don't understand what I get. >From Wolfram (http://mathworld.wolfram.com/SphericalHarmonic.html), Re_Y11.png, Im_Y11.png & mod_Y11.png seems to be correct http://fredantispam.free.fr/Re_Y11.png http://fredantispam.free.fr/Im_Y11.png http://fredantispam.free.fr/mod_Y11.png when I use r = (sqrt((2*n+1)/4.0/pi)*exp(0.5*(gammaln(n-m+1)-gammaln(n+m+1)))*sin(phi)*exp(1j*m*theta))**2 But when I use special.sph_harm(m,n,theta,phi), I get this http://fredantispam.free.fr/Re_Y11_2.png http://fredantispam.free.fr/Im_Y11_2.png http://fredantispam.free.fr/mod_Y11_2.png Real & imaginary parts don't seem to be correct. What I'm doing wrong ? Cheers, Here the small code I have used. from sys import argv from scipy import pi, cos, sin, exp, sqrt, mgrid, real, imag from scipy.special import sph_harm, gammaln from enthought.tvtk.tools import mlab, ivtk def main(): m = int(argv[1]) n = int(argv[2]) gui = mlab.GUI() window = ivtk.IVTKWithCrustAndBrowser(size=(1175,773)) window.open() fig = mlab.Figure(window.scene) o = mlab.Outline() fig.add(o) dphi, dtheta = pi/180, pi/180 [phi, theta] = mgrid[0:pi+dphi:dphi, 0:2*pi+dtheta:dtheta] ### cf. Wolfram : theta <--> phi r = real(sph_harm(m,n,theta,phi))**2 # r = real(sqrt((2*n+1)/4.0/pi)*exp(0.5*(gammaln(n-m+1)-gammaln(n+m+1)))*sin(phi)*exp(1j*m*theta))**2 x = r*cos(theta)*sin(phi) y = r*sin(theta)*sin(phi) z = r*cos(phi) s = mlab.Surf(x, y, z, z) fig.add(s) window.scene.x_plus_view() window.scene.camera.parallel_projection = True window.scene.camera.azimuth(-62) window.scene.camera.elevation(19.5) gui.start_event_loop() if __name__ == '__main__': main() -- Fred.

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Shooting method in scipy
by Nils Wagner Aug. 22, 2006

Aug. 22, 2006

Hi all, Has someone implemented the shooting method in scipy ? Nils

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vectorized atan
by Ryan Krauss Aug. 22, 2006

Aug. 22, 2006

I know this is a dumb question, but it seems like scipy must have a vectorized atan and atan2 somewhere. I can't seem to find it though and am using list comprehensions on the functions from the math module. Am I missing something? Ryan

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import linsolve.umfpack failure
by Jon Willits Aug. 21, 2006

Aug. 21, 2006

I have installed scipy on an Intel Mac (running python 2.4.3) using the ScipySuperpack-Intel-10.4.tar. Everything seems to have installed ok, except that when I import scipy, I get this message: import linsolve.umfpack -> failed: Failure linking new module: / Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site- packages/scipy/sparse/sparsetools.so: Library not loaded: /usr/local/ lib/libgfortran.1.dylib Referenced from: /Library/Frameworks/Python.framework/Versions/2.4/ lib/python2.4/site-packages/scipy/sparse/sparsetools.so Reason: image not found I noticed an earlier posting about this, with a message that said something like "oops, bad linking" but without any advice on how to fix it. My programs run fine (they do not rely on the sparse libraries), but always produce that error message, which will not be good for all kinds of reasons. Is there a way to fix this, or at a minimum, to suppress this error message? Thanks, Jon Willits

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Sparse matrices and weave.inline, f2py or Pyrex
by William Hunter Aug. 21, 2006

Aug. 21, 2006

List; Has anyone ever attempted using sparse matrices in combination with either one of the following; weave.inline, f2py or Pyrex? What is the best option? Perhaps a case of personal preference? Reason I'm asking: I've gotten the solving part of my code to run satisfactorily, but building them with Python's for loops takes a heck of a long time, too long. Regards, William

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p-values of simple regressions
by Riccardo Corradini Aug. 21, 2006

Aug. 21, 2006

Dear scipy users, I would like to compute the p-values to accept of reject the null hypothesis of a simple ordinary least square regression. Which is the scipy's function for the t of student(and p-values)? Could somebody please give me an example? Thanks a lot in advance Respectfully Riccardo Chiacchiera con i tuoi amici in tempo reale! http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com

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