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Forum: Fields: Magnetic and Otherwise
Re: None Getting NAN for values of Point in a magnetic field class (Aaron Liblong)
Re: Feedback Re: Getting NAN for values of Point in a magnetic field class (Gumplinger Peter)
Re: None Re: Getting NAN for values of Point in a magnetic field class (Aaron Liblong)
Re: Feedback Re: Getting NAN for values of Point in a magnetic field class (Gumplinger Peter)
Date: 18 Jul, 2012
From: Aaron Liblong <Aaron Liblong>

So it turns out the NAN problem was entirely a result of trying to calculate the field at the origin. Thanks for noticing that! However, there is still some weird behaviour. The main problem is that when I set the field to a constant value, after the first step it no longer remains constant (though only slightly different). For example:

 x, y, z: 20.5879; 18.6825; 19.6499
sin(theta), cos(phi): 0.816612; 0.740544
Br, Btheta, Bphi: 0; 1e-05; 0
Bx, By, Bz: 4.27432e-06; 3.87874e-06; -8.16612e-06
previous Bx, By, Bz: 4.27432e-06; 3.87874e-06; -8.16612e-06
x, y, z: 27.5898; 24.5526; 26.1012
sin(theta), cos(phi): 0.816644; 0.747029
Br, Btheta, Bphi: 0; 1e-05; 0
Bx, By, Bz: 4.31141e-06; 3.83679e-06; -8.16644e-06 <---------------

(next step)
    1     29.5       25     23.5      0.99  0.00685     45.4      45.4    hallPhys eIoni

previous Bx, By, Bz: 0.9341733459286579; -0.1875870402351953; 0 <------------
 x, y, z: 29.51563709455589; 25.02548071971535; 23.5374965955675
sin(theta), cos(phi): 0.8543663692038602; 0.762739708814276
Br, Btheta, Bphi: 0; 1e-05; 0
Bx, By, Bz: 3.963738238545995e-06; 3.360742461663736e-06; -8.543663692038603e-06 <-----------------
previous Bx, By, Bz: 0.06666666666666667; 1.086944420850742e-322; 1.491668146240041e-154 <-----------------
x, y, z: 34.91789711328752; 29.70973367563871; 29.3859584436884
sin(theta), cos(phi): 0.8419042269305184; 0.7616214773706649
Br, Btheta, Bphi: 0; 1e-05; 0
Bx, By, Bz: 4.109914943017864e-06; 3.496902404816453e-06; -8.419042269305184e-06
previous Bx, By, Bz: 4.109914943017864e-06; 3.496902404816453e-06; -8.419042269305184e-06

This also highlights an instance of the values initially stored in the field matrix not matching what they were previously set to. This only seems to happen around the beginning of a new step (including at the very start of the simulation, where it contains very small non-zero values). Do you know what could be causing this, and does it seem like a problem? I'm not sure if these values are used for anything after being changed, or are just sitting idly in the matrix before being recalculated.

Other than that, you mentioned that problems may be arising because I'm using an unphysical field/particle setup. Just for the sake of the simulation, shouldn't I be able to simulate a physically impossible field (such as a magnetic monopole)? Or does the G4 particle tracking rely on a field that more or less satisfies Maxwell's equations?

Many thanks,
 Aaron

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1 Feedback: Re: Getting NAN for values of Point in a magnetic field class   (Gumplinger Peter - 18 Jul, 2012)
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