This probably belongs in the chat forum, but The thread about speed of matrix times vector, comparing MATLAB and J, has interesting and useful comments, but as an educator I am impatient with this type of comparison.
To a math professor, J's strength is its array point of view, its well-conceived array operations, and the pleasure of thinking in J. MATLAB's strength is its linear algebra and differential equations routines and its competent interface to Maple's symbolic algebra. I wish Jsoftware could afford to spend the level of effort on linear algebra and differential equations that it has put into plotting. Then more professors and students might discover J as a tool for mathematical thought. Kip Murray Math, University of Houston, Retired On Thu, 8 Nov 2007, Joey K Tuttle wrote: At 11:56 -0800 2007/11/08, Roger Hui wrote: > > There isn't a built in function that > > j uses to generate normal distributions, and writing an equivalent > > to MatLab randn() would be an interesting exercise. > > >From http://www.jsoftware.com/jwiki/Essays/Normal_CDF > erf =: (1 H. 1.5)@*: * 2p_0.5&* % ^@:*: > n01cdf=: -: @ >: @ erf @ %&(%:2) > > Whence an approximation to randn: > ny=: n01cdf nx=: i:5j2000 > randn=: nx {~ ny I. [EMAIL PROTECTED]&0 > Lovely! In praise for DOJ, erf and n01cdf are given on the H. page (although I didn't immediately think to look there :) There are a couple of subtle differences from the ones above, DOJ doesn't include the, apparently redundant, parens of your erf and n01cdf differs a bit, but their results are very close with no greater than 4.996e_16 difference in your example. In any case, thanks for the exposition -- certainly in the case of timing the original inner product, the generation of the random normal distributions should be excluded from the timing (as they were in MatLab). ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm Kip Murray [EMAIL PROTECTED] http://www.math.uh.edu/~km ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
