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For certain dipole locations (and moments) FSM calculates NaN potential at certain electrodes. It is probably due to numerical error in calculating `cos(phi)` value which violates `-1 <= cos(phi) <= 1`, thus leading to `arccos(cos(phi))` being NaN.
`cos(phi)` fixed if violating `-1 <= cos(phi) <= 1`. If `abs(cos(phi)) > 1 + 1e-10`, `RuntimeWarning` is triggered. See also: f78145b
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We discovered the same problem in the LFPy-version of the code. This problem occurs when phi is not defined. I.e., when theta= 0 or theta = pi or when the dipole has no tangential component. Here: LFPy/eegmegcalc.py, from line 646, you can see how we solved this by creating a mask to avoid trying to compute phi when not defined. The way the dipole is decomposed in a radial and tangential component, is prone to round-off errors. We have created a unit vector containing the direction of the dipole location vector (self._z, line 400), and using self._z to decompose the dipole (line 545) will reduce the risk of round-off errors. |
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For particular combination of dipoles and electrodes calculated potentials were NaNs.
I have traced the error to violation of the
-1 <= cos(phi) <= 1constraint, probably due to a numerical error.