Re: Map
- To: mathgroup at smc.vnet.net
- Subject: [mg130920] Re: Map
- From: Bob Hanlon <hanlonr357 at gmail.com>
- Date: Sat, 25 May 2013 05:40:39 -0400 (EDT)
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hklist = Array[h, {5, 3}]; bragg = {b1, b2, b3}; qbarlist = Map[(# - bragg) &, hklist, {2, 2}]; As stated in the documentation ( http://reference.wolfram.com/mathematica/ref/Map.html ), the third argument to Map is the level specification and the form {n1, n2} specifies levels n1 through n2. In this case n1 and n2 are equal so it is equivalent to just {n1}. qbarlist === Map[(# - bragg) &, hklist, {2}] True If you look at your outputs carefully you will see that you do not get the same result with a third argument of {1} qbarlist === Map[(# - bragg) &, hklist, {1}] False qbarlist // Dimensions {5, 3, 3} Map[(# - bragg) &, hklist, {1}] // Dimensions {5, 3} Examine the two different arrays above to understand the different behavior. Bob Hanlon On Fri, May 24, 2013 at 6:25 AM, Jon Morris <djpmorris at googlemail.com>wrote: > I'm new to Mathematica and I've been given some code to help me analyse > some data. I'm trying to understand what the Map function does, > specifically what the {2,2} means? > > qbarlist = Map[(# - bragg) &, hkllist,{2, 2}]; > > hklist is a 3 column list, bragg is a three element vector. > > When I try the same line with {2} or {1} I seem to get the same answer. > The online explanation of this term does not make that much sense to me. > I'd be very grateful if someone could explain the purpose of the last term > of the Map syntax. > > Thanks, > Jon > >
- References:
- Map
- From: Jon Morris <djpmorris@googlemail.com>
- Map