Eugine_Nier comments on Welcome to Less Wrong! (2010-2011) - Less Wrong

42 Post author: orthonormal 12 August 2010 01:08AM

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Comment author: Eugine_Nier 17 December 2010 09:31:57PM 2 points [-]

There are two functions that are their own second derivative, and four which are their own fourth derivative.

More precisely there is a 2-dimensional parameter space of functions that are their own second derivative, i.e., any function of the form Ae^x+Be^-x for any constants A and B.

Comment author: drc500free 17 December 2010 10:29:02PM 1 point [-]

Is there a generic form of that for any nth derivative?

Comment author: Eugine_Nier 17 December 2010 10:34:08PM 2 points [-]
Comment author: JGWeissman 17 December 2010 10:36:01PM *  1 point [-]

Sum over integers k from 1 to n of A(k)*e^(e^(2*i*pi/k)*x) is its own nth derivative, for all A.