Mathematica

syntax extension
Is there a neat way to create a new symbol, say /!. so that expression /. BetterRules[rules] could be written as expression /!. rules I do not find writing something like (expression) ~BR~ (rules) to be quite adequate, especially with the extra parentheses. RJF ... 14 Jan 2010 06:50

restricting interpolating functions to be positive
Hi All, I would like to construct an interpolation that can only take on positive values. The data that I'm trying to interpolate is all positive, but for some reason the Interpolation[] function 'wants' to connect the dots by dipping below zero. Is there a way to force positivity? Or should I simply adjust t... 18 Jan 2010 03:10

Rotate
Re 7.0.1 under WinXP. Rotating the result of GraphData is easy, but how to title it? I haven't found a helptext example but guided by those found, my attempt below yields the message "Graphics is not a Graphics primitive or directive." Thanks. Bruce Graphics[Rotate[ GraphData@{"CompleteTripartite... 13 Jan 2010 06:30

ODE Stiff Systems
I am trying to solve an ODE numerically using NDSolve but get a message " step size is effectively zero; singularity or stiff system suspected." Can anyone please suggest an otion I can use along with 'Method' to attempt to overcome the problem? I have tried Method -> "ExplicitRungeKutta" and it doesn't work. ... 11 Jan 2010 06:29

NonlinearModelFit and ParameterTable
mtest1[t_,ltime_]:=If [var1*(t+var2-qtime)>8000,Sum[If [var1*(tsum +var2-qtime)>8000,8000*(1-P),var1*(tsum+var2- qtime)*(1-P)],{tsum,t- ltime+1, t,1}],Max[{Sum[{var1*(tsum+var2- qtime)*(1-P)},{tsum,t-ltime +1, t,1}]},0]]/156000 i optimize the model above with: parameter2= NonlinearModelFit[ExpData, mtest1[... 15 Jan 2010 03:53

Occurrences in Mathematica
Hi, I have a very big list of elements and I need Mathematica to give me only those elements which occure only once... Could anybody advise me please how to write the code for that? Thks much George ... 12 Jan 2010 08:02

export differential equation solution obtained
In your first equation (after "=" is replaced by "=="), you used p[t] in both terms. I changed the second to n[t] sol3 = NDSolve[{ p'[t] == -0.0491*p[t] - 0.0089*n[t], n'[t] == 0.0491*p[t] + (0.0491 - 0.0089)*n[t], p[0] == 25000, n[0] == 0}, {p, n}, {t, 0, 100}][[1]]; Plot[Evaluate[n[t] +... 10 Jan 2010 04:14

export differential equation solution obtained through Mathematica
Hi, obviously the output of NDSolve is a numerical function not an anayltical one. Therefore, the best you can do is to create a table with p and t values. This data you may the export e.g. to a CSV (or other formated), file that can be read by EXCEL. Here is an example: sol = f /. NDSolv... 8 Jan 2010 07:10

horizontal line color
Hi All, Does anyone know how to change a color of the horizontal line inserted below or above the cell? I can't figure it out and there is nothing about it in the documentation center and in the group. Cheers Anna ... 13 Jan 2010 06:31

Print Registration Marks
Can someone recall where I saw an article by Wolfram on how to lay out pages, graphics etc. I recall seeing a diagram with print registration marks and some idea of how to use printer points etc. I thought it was one of the tutorials but cant find it ..... ... 8 Jan 2010 05:00