Re: Use of delayed assignment, :=, with a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg91788] Re: Use of delayed assignment, :=, with a list*From*: "David Park" <djmpark at comcast.net>*Date*: Sun, 7 Sep 2008 22:55:03 -0400 (EDT)*References*: <ga077v$oto$1@smc.vnet.net>

You don't give us the precise code that causes the problem. But, in any case, instead of doing direct assignment of the elements, why not define an opticalMatrix with parameters. I suspect those are the things you would actually be working with. opticalMatrix[f_, zomeasure_] := {{1, zomeasure}, {-(1/f), 1 - zomeasure/f}} Then you can directly multiply two matrices as follows: opticalMatrix[f1, z1].opticalMatrix[f2, z2] // Simplify {{1 - z1/f2, z1 + z2 - (z1 z2)/f2}, {-((f1 + f2 - z1)/(f1 f2)), (f1 (f2 - z2) + z1 z2 - f2 (z1 + z2))/(f1 f2)}} It is always better to localize parameters or variables to a definition by using arguments than having them floating around free in your notebook. -- David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ "phillman5" <PHILLMAN5 at gmail.com> wrote in message news:ga077v$oto$1 at smc.vnet.net... >I use simple 2x2 matrixes for each item in a optical train to get the > over all 2x2 matrix. The four elements are a, b, c, d, and I can > assign them easily in one step. > > {{a, b},{c, d}} = any 2x2 matrix > > however some times the rhs has variables, so I'd like to use an > delayed assignment > > {{a, b},{c, d}} := any 2x2 matrix > > this does not work, Mathematica says the two lists are not the same > shape. In particular: > > {{a, b},{c, d}} := {{1, zomeasure}, {-(1/f), 1 - zomeasure/f}} > > where f and zomeasure are variables (maybe not even defined yet). > Mathematica says the lists are not the same shape, but if I use an > assignment operator there is no problem. I am not completely > convinced it is a mere Mathematica notation misunderstanding on my > part because a simpler 2x2 assignment: > > {{q, g}, {h, k}} := {{f, w}, {r, t}} > > works. (Mathematica does respond {{Null, Null}, {Null, Null}}, but g > does have a delayed assignment of w. > > Is there an easier way to do a delayed assignment than each member, a, > b, c, d individually > > tempmatrix := {{1, zomeasure}, {-(1/f), 1 - zomeasure/f}} > a := tempmatrix[[1]][[1]] > b := . . . > >