Questions on assigning and unassigning definitions to names that represent them, including issues raised by context and localization. Use tag [assignment] for issues relating to Set versus SetDelayed.
61
votes
7answers
2k views
What are the use cases for different scoping constructs?
Mathematica includes three functions that I know of which can be used to effectively (if not actually) define a variable and give it a value within a local scope: ...
30
votes
3answers
668 views
Why modules with no variables?
I was reading some code, in particular, recipe 4.13 on unification pattern-matching in Sal Mangano's Mathematica Cookbook, and there were many instances of Modules with no variables in them, such as
...
27
votes
3answers
648 views
Is there an equivalent of MATLAB's Workspace window in Mathematica?
For example, in MATLAB, a panel is available where one can see straightaway which variables are used and their dimension sizes. Is such a feature available in Mathematica? I really find it hard to ...
17
votes
1answer
775 views
How to define a global variable in Mathematica?
I have restricted the context of my notebooks to each individual notebook. So variables in each notebook are local and are not seen in another notebook.
But in two of my notebooks I have two ...
15
votes
5answers
3k views
How do I clear all user defined symbols?
Is there some way to do this other than going to Evaluation -> Quit kernel and firing a new one up?
14
votes
3answers
399 views
Create an adaptive amount of local variables for error propagation
I intend to write a function which calculates the result and the error for any formula with any amount of variables using the Gauß Error Propagation.
The error $dR$ for a function $R(a,b,c)\,$ and ...
14
votes
6answers
884 views
Why can't I define vector v as having subscripted elements v_1, v_2, v_3…?
I'm a very beginner in Mathematica 8 programming. While trying to play a little with tensor analysis I encountered a problem. How to define for example vector in such manner:
v={$v_1,v_2,v_3$}
For ...
12
votes
4answers
942 views
Clear complains that a variable is not a symbol or a string?
Here's a small listing where I've used EscqEsc to typeset θ in the notebook:
...
12
votes
6answers
335 views
How to clear all variables except one?
I have a lot of variables: $a,b,c,d, \ldots $
I want to clear the values of all of them except $b$. It's really lengthy to write
Clear[a];
Clear[c];
...
Is ...
12
votes
4answers
427 views
Making a symbol's new definitions be tried before all previously defined ones
Is there any way to "close" a package (or a symbol, or a context) in that if a user of the package adds definitions to the symbol they will be tried before the package defined ones, just like what ...
12
votes
1answer
143 views
Is it possible to Clear all variables (but not functions)?
I have written a Mathematica script in which I define functions and variables. Here is a vastly simplified example:
...
11
votes
7answers
482 views
How to Set parts of indexed lists?
I would like to assign a list to an indexed variable and then change it using Part and Set like this:
...
10
votes
4answers
249 views
How to use pattern matching to assign values to Subscript[f,x_]?
I want to define two subscripted functions Subscript[f,1] and Subscript[f,2]. To keep the assignments local, I would like to ...
10
votes
3answers
226 views
How can I hold UpValues but evaluate other expressions?
Consider these definitions:
own = "OwnValue";
down[_] = "DownValue";
sub[_][_] = "SubValue";
N[n] = 3.14;
_[___, up, ___] ^= "UpValue";
The attribute ...
10
votes
1answer
186 views
What is $ sign in Mathematica?
Is it a special sign or it can be used as anything else? For creating variables for example.
$x=4
9
votes
3answers
465 views
How to use local variables with indices in a Mathematica Block environment?
I have the following code:
Subscript[f, i_][x_] := Block[{a},
Subscript[a, i] = 3 x;
Subscript[a, 1]
]
If I evaluate for example ...
9
votes
4answers
357 views
how to differentiate formally?
I have been wrapping my head around this for a while now and I have not found a solution so far.
I want to work with an arbitrary number of variables in mathematica and use some built in functions.
...
8
votes
3answers
314 views
Variable variable names
I have two variables, $ u \in \{0,40\}$ and $\gamma \in \{0,1\}$. I take $10$ values of $u$ and $5$ values of $\gamma$ and using their combinations as a pair of input parameters, I perform some ...
8
votes
3answers
222 views
Problem when defining variable in Mathematica
I'm trying to run this:
domain := {n, 0, 10};
Plot[n, domain]
but it doesn't work. Instead, it generates the message
...
8
votes
2answers
139 views
Representing a value in an output as a self defined variable
I'm trying to find a way to have Mathematica always represent a numerical value as a self defined variable that I define using lhs=rhs. For example, if I execute
...
8
votes
1answer
107 views
Different behaviours of Default Argument
I don't really understand the behaviour of Default Argument. If I execute this command in Mathematica:
In: {f[a], f[a + b]} /. f[x_ + y_.] -> p[x, y]
...
7
votes
3answers
378 views
Elegant manipulation of the variables list
I have a list of global variables (some of them are indexed variables), for example:
varsH = Hold[U0[1], U0[2], B0, V0[1], V0[2]]
Or (if it is easier to handle) ...
6
votes
2answers
159 views
Can I redefine a list as a set of variables?
Suppose I have a list
mydata = {3, 14, 15, 92, 65}
and in some cases I want to manipulate it as a list, like for reading from and writing to a file, or for ...
6
votes
4answers
541 views
Define a mathematical set
I have a terribly short question:
Is there a way to define a pure mathematical set?
I tried a bit of googling, but the word "set" has two meanings and the other one (as in setting) as by far more ...
6
votes
2answers
196 views
How to choose variables from a list for a function and then use the solution in a subsequent function?
I am trying to calculate heating degree days and cooling degree days and output that information to a table. I am using mathematica's curated data to do this. In text this is what I would like to ...
5
votes
5answers
334 views
Using a built-in symbol as a variable
I want to produce a Mathematica Computable Document in which N appears as a variable in my formulae. But N is a reserved word in ...
5
votes
3answers
541 views
Assigning values to a list of variable names
As part of a calculation I need to do something like this
Evaluate[{aaa, bbb, ccc}[[ index]]] = {1, 2, 3, 4, 5}
so if index is ...
5
votes
1answer
90 views
Reloading package after accidental Remove[] of symbol
I was using Needs["PlotLegends"] By chance I removed ShowLegend by Remove[ShowLegend]
How do ...
5
votes
1answer
97 views
Proper use of arbitrary number of variables
So, I'm working on a project where the number of independent variables is not fixed.
Consider a problem of $N$ independent variables, $\boldsymbol{r}$.
I want to perform different things with them. ...
5
votes
1answer
89 views
Proper localization of variable names
In functions like NonlinearModelFit I need to specify parameters with a symbol name. If I localize these parameters they get cluttered in the output (e.g....
5
votes
1answer
67 views
Why doesn't DumpSave work for elements created within a local notebook context?
I recently noticed that when dealing with notebooks with local context, I cannot successfully DumpSave variables, or, rather, when I call ...
4
votes
3answers
278 views
How to Clear variables with apostrophe?
An apostrophe ' is often used when we want to distinguish two variables. For example, if we already have a variable t and we may ...
4
votes
1answer
111 views
Module with “local functions”
I am trying to use a Module having "local functions", i.e., those which I need to define only inside this module.
So I tried this:
...
4
votes
4answers
117 views
Put local variables for Block in a variable [duplicate]
Is is possible to assign {x = 2, y = 3, z = 4} to a variable var so that one can write
...
4
votes
2answers
263 views
How to create a Table of Tables with indexed variables
I want to use concise code to generate a table of values that list the addition of a set of vectors. What I am looking for is essentially a Table of Tables.
I will show here the kind of lists I want, ...
4
votes
2answers
74 views
Creating functions from output of other calculations
Apologies in advance if the title is vague, I'm not really sure what to call this.
I have a function (call it 'foo') that generates a largeish polynomial, and it is natural to make the variables be
...
3
votes
2answers
202 views
Mathematica does not understand (R^3)^(1/3) is the same as R [closed]
In the output from a calculation in mathematica stands a/((R^3*c)^(1/3)), with c and a ...
3
votes
1answer
117 views
Using external variable as a variable inside WhenEvent & NDSolve
I'm trying to use the new WhenEvent functionality of NDSolve in Mathematica 9, in order to perform an action when a variable in the system reaches a certain value. I would like this variable to come ...
3
votes
1answer
97 views
How to replace variables in an expression?
I have generated a matrix using Mathematica,
$\left(
\begin{array}{ccc}
\text{cos$\theta $} & -\text{sin$\theta $} & \text{cos$\theta $}\, \text{dx}+\text{dx}-\text{dy}\, \text{sin$\theta $} ...
3
votes
2answers
125 views
Save variables values and definition
I used to do a lot of programming in R and recently switched to Mathematica. One thing that bothers me is that I haven't found a way to save variables, their values and definition!
Let's look at an ...
3
votes
1answer
87 views
Is it safe to assign a variable and function of the same name for different things?
I'm writing out a notebook that goes through the van der Waals Equation of State for gases, and I run into a situation where I want to assign (simplified) Tc[b_]:=5b, use that to solve for b in terms ...
3
votes
1answer
129 views
How to restrict global variables to within a given notebook? [duplicate]
Possible Duplicate:
Is there a way to separate variables between multiple notebooks?
I assigned a global variable like a=10; It works in all my ...
3
votes
0answers
58 views
What's reliable way of finding declared but undefined functions/symbols in several interrelated packages?
I have many packages some of which use some of others. I have many symbols defined in them. Is there a reliable way of finding declared/exported but undefined functions/symbols in several ...
2
votes
2answers
268 views
Global variable initialization in packages
Is it a good idea to Initialize variables globally inside a package ?
will they be local by default to that package ?
2
votes
3answers
145 views
how can I generate a sequence of assignments?
I want to make a sequence like follows
r[1]=
r[2]=
r[3]=
r[4]=
....
r[n]=
The above r[i] represents coordinates which I have ...
2
votes
1answer
184 views
Can I create a dynamic number of rows in TabView through an iteration?
I have written code, with the help of stackoverflow of course, and I want to make it user friendly so that other people in my lab can use it. I'm playing with DialogCreate and similar functions. I ...
2
votes
2answers
191 views
local variable naming & symbolic argument
I'm stuck here with my variable assignment in this scenario
...
2
votes
1answer
63 views
Strange behaviour of variables in Table
I'm trying to work with some vectors and have run into a strange problem. An obvious way to define a difference of two vectors would be
dif[x_,y_] := x-y
I ...
2
votes
2answers
241 views
defining recursively a function with multiple if conditions
I am trying to recursively define a function which satisfies the following system of equations and which depends on two parameters $n$ and $l$,
$$
\begin{align}
A(x, n, l) &= F[ A(x,n-1,l) ]\\
...
2
votes
3answers
140 views
How to make a defined symbol stay in symbol form?
How to make a defined symbol stay in symbol form?
w = 3; g = 4;
{w, g}[[2]]
3
I want the output to be ...
