On 26 September 2013 10:02, Daπid <davidmen...@gmail.com> wrote: > The simplest way is to do it in cartesian coordinates: take x, y, and z > independently from N(0,1). If you want to generate only one normal number > per step, consider the jacobian in the angles.
Actually, this is wrong, as it would allow displacements (at 1 sigma) of 1 along the axis, but up to sqrt(3) along diagonals. What you actually want is a multivariate normal distribution with covariance proportional to the identity (uncorrelation between axis and isotropy). See formulae here: http://en.wikipedia.org/wiki/Multivariate_normal_distribution
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