Date: May 25, 2013 5:33 AM
Author: Bob Hanlon
Subject: Re: Map
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@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

>

>