Weird singularities/cylindrical & spherical coordinates

AI Thread Summary
The discussion highlights the behavior of a vector function in cylindrical coordinates, which has a singularity only at the origin. In contrast, when expressed in spherical coordinates, the function exhibits singularities along the entire z-axis, specifically when θ equals 0 or π. This discrepancy arises from the realization that in cylindrical coordinates, the condition ρ = 0 includes the z-axis. The confusion stems from the different interpretations of singularities in the two coordinate systems. Ultimately, the issue was clarified by recognizing the relationship between the coordinates and their singularities.
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If you consider the vector function (expressed in cylindrical coordinates)
<br /> \frac{1}{\rho} \hat{\phi}<br />
where \rho = \sqrt{x^2+y^2}, you notice it has a singularity at the origin ONLY. But if you express this in spherical coordinates, what you get is
<br /> \frac{1}{r\sin \theta} \hat{\phi},<br />
which is singular whenever \theta = 0 or \theta = \pi; that is, on the entire z axis! (I got this by just substituting the identities x = r\sin \theta \cos \phi and y = r \sin \theta \sin \phi into the above expression for \rho.) How can this be? I'm doing something wrong, but what?
 
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Uhhh...sorry, I was being really dumb. \rho = 0 includes the z-axis in cylindrical coordinates. FML.
 
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