In a letter to Nature (Ford G W and O'Connell R F 1996 Nature 380 113) we presented a formula for the derivative of the hyperbolic cotangent that differs from the standard one in the literature by an additional term proportional to the Dirac delta function. Since our letter was necessarily brief, shortly after its appearance we prepared a more extensive unpublished note giving a detailed explanation of our argument. Since this note has been referenced in a recent article (Estrada R and Fulling S A 2002 J. Phys. A: Math. Gen. 35 3079) we think it appropriate that it now appear in print. We have made no alteration to the original note.
Publication Source (Journal or Book title)
Journal of Physics A: Mathematical and General
Ford, G., & O'Connell, R. (2002). Note on the derivative of the hyperbolic cotangent. Journal of Physics A: Mathematical and General, 35 (18), 4183-4186. https://doi.org/10.1088/0305-4470/35/18/313