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.

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3
votes
2answers
150 views

Bare symbol invocation fails but not if used with an argument

How to achieve the following behavior on a symbol f? Background: The main goal is to use the symbol to tag an abstract data structure where downvalues are used to store information. Only defined ...
0
votes
2answers
149 views

Define a function on a parameter argument set to zero

Say I have an expression (matrix) that depends on several variables. f= {{a, b+c},{2a-b^2,c^5+a b}} I want to define new matrices with the single parameter ...
0
votes
0answers
39 views

Varying number of function arguments [duplicate]

I have a function of six arguments: ffit[q1_, q2_, q3_, q4_, q5_, q6_] := (a1*q1^2 + a2*q2^2 + a3*q3^2 + a4*q4^2 + a5*q5^2 + a6*q6^2) ...
1
vote
0answers
72 views

Why the variable cannot use subscript? [duplicate]

Today,I use the Lagarange method to deduce the robot 's dynamic equation .I use the mma to help me calculate. I want to use $$x_B,y_B, v_{Bx}, v_{By}, v_B ^2$$ to represent the point B 's ...
0
votes
1answer
85 views

Circumventing the default scoping: Assign a variable inside a function [duplicate]

I'm currently trying very hard to assign a variable inside a function. Therefore I'm using a function like this, which should reassign a predefined variable. ...
20
votes
3answers
413 views
1
vote
1answer
190 views

Is linear interpolation applicable here

From my understanding about Linear Interpolation especially of that of Newton's Divided Difference Polynomial, we could get the value of F(x) from the given set of ...
6
votes
1answer
170 views

How can I define a ⊕ operator?

What is wrong with the following code? CirclePlus := SparseArray[Band[{1, 1}] -> {##}] & a_ ⊕ b_ := CirclePlus[a, b] SetDelayed::write: Tag Function in ...
4
votes
1answer
180 views

Forcing Mathematica to recognize a symbol without defining it

In the Mathematica front-end, symbols that have been defined are colored black and symbols with no definition associated are colored blue. This is useful to prevent spelling mistakes. Also, defined ...
8
votes
2answers
333 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
1answer
234 views

What does it mean when a function is defined with two pairs of brackets

I have noticed a function defined as such: f[x_][y_] := expr; How is the argument y in 2nd pair of brackets being used? What is the difference from defining a ...
10
votes
4answers
803 views

Refering to global variables inside modules

How do I refer to global variables inside modules if the same name is used for a local one? In code, I want that ...
3
votes
3answers
130 views

Using a variable to tell Mathematica which existing variable to manipulate

I have an estimation routine I have coded up, I want now to do some tests on it where I pick a particular parameter and run the estimation for differing values of that parameter. What I want is to be ...
0
votes
0answers
152 views

NIntegrate with an arbitrary number of variables [duplicate]

I need to evaluate NIntegrate with a variable number of variables. Here's a concrete example. I'll accept an answer that finds a way to make the example work. I ...
3
votes
2answers
164 views

Assigning an equation as a variable

I am compiling a calculator where many slider parameters are used to define a value, where the defined value may then be reused to define another value. I am unable able to, or at least been ...
25
votes
5answers
3k views
0
votes
0answers
42 views

Subscripts to a variable; why a letter shoud come before a digit?

I noticed that I cannot create a variable $f_{2s}$ since Mathematica seems to leave a space between the subscripts 2 and s ...
1
vote
2answers
140 views

Add a letter to a variable name from a list

Basically I am searching for a way to add the letter u to an existing list of variables {a,b,c,d} to obtain the variable list ...
0
votes
1answer
83 views

Collecting variables from Subscript

I have followings set: t = Transpose[{x[#] & /@ Range[20], RandomInteger[15, 20]}]; Subscript[#[[1]], #[[2]]] & /@ t The code is just to build my set.So ...
4
votes
2answers
492 views

Table of Variables

I use a list of variables {x1, x2, x3} to Solve a particular set of equations. I am now trying to generalise this depending on ...
2
votes
1answer
94 views

What is the need for function parameters? Many possible inputs

If I have many possible variables related to one another, why do I need to define my function with parameters for plotting? For example, if I have an equation like: ...
4
votes
1answer
238 views

Define a function with the condition that it must be positive

I have a function f(x) and I want to define a new function g(x) that is equal to f(x) only ...
2
votes
5answers
231 views

Treat list as cyclic

I am considering the following case. Say that T={p1,p2,p3} represents a triangle. In addition, I want to parameterize the edges of the triangle ...
1
vote
0answers
1k views

How to assign (and retrieve) variables with subscripts? [duplicate]

I like to give subscripts to my variable names when the variables are related. I.e., Subscript[r, i] = 3 3 A problem arises when I later assign ...
12
votes
5answers
2k 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 ...
1
vote
3answers
134 views

Declare local variable when defining a function to mimic Table[]

The problem: I want to define a function tab to replace the long line Table[f[i,j,k,l],{i,3},{j,3},{k,3},{l,3}] by a shorter ...
2
votes
2answers
114 views

Extracting variables from Hold expression

For example I have some global assignments x=1;y=2;z=3 and an expression Hold[x*y/z]. How can I now extract variables ...
3
votes
2answers
255 views

How to declare a function that uses local variables of a module outside this module?

I have the following code Module[{f,x=0}, f[t_] := x + t; ..........; ...f[1]...; ..........; ] My aim is to put the declaration of the function ...
7
votes
2answers
688 views

Obtaining the name of a variable as a string [duplicate]

Suppose that I have an arbitrary variable myVariable. Is there some function fun -- either built-in or one that I can define -- ...
2
votes
1answer
133 views

Reuse local variable in declaration within With [duplicate]

Considering the richness of Mathematica.SE, I am quite surprised I could not find my answer... I am very sorry if it is a duplicate. Consider the following example: ...
-2
votes
2answers
236 views

Mathematica not assigning variable correctly

So I have been fiddling with this the last hour and I just can't get it to work. I have 3 matrices of the same size which contain nothing but 0's in a list, I also have 3 matrices of the same size ...
8
votes
3answers
178 views

Protecting function definitions only for particular inputs

I would like to be able to define the values of a particular function for new inputs. f[x1]=f1; f[x2]=f2; I would also like to be able redefine the values for ...
20
votes
2answers
372 views

The dangers of SaveDefinitions — should this really happen?

I have been bitten hard by SaveDefinitions -> True. I'll describe in detail what happened below. My questions are: Is this a bug? What is the most convenient ...
1
vote
1answer
257 views

Print indexed (by subscript) variable name systematically

I have some variables : Subscript[S, 1], Subscript[S, 2]...etc. But they are defined in a for loop like For[g = 1, g < 4, g++, Subscript[S, g] = g]; Later, I ...
13
votes
3answers
439 views

Variable scope similar to other languages

Mathematica, unlike many other languages, defines the variables in the global scope unless it is explicitly asked to define a variable in a local scope, e.g., using ...
3
votes
1answer
263 views

Evaluating a function on permutations of its arguments

Say I have a function "temp" of $n+1$ variables, $y,z1,z2,z3,...,zn$. I want to test if my function has certain symmetries like swapping $y$ with square of any $z$, swapping any two of the zs, ...
0
votes
1answer
109 views

Arbitrary number of variables in Module, Block, etc

How do I specify an arbitrary number of variable names and initialize them inside of a Module or Block? For example, I want to do something like: ...
0
votes
0answers
133 views

How to define a variable as a function of another variable?

I want to define a variable q which is a function of t. And I want to define another variable ...
1
vote
0answers
174 views

Variable scope in nested NMaximize, NMaxValue

I'm trying to use NMaxValue inside other statements (FindRoot and NMinimize). Those statements should bind variable names, but I'm getting weird warnings which seem to indicate that the variables ...
7
votes
1answer
160 views

Specifying optional arguments with variables

Perhaps this is poor programming on my part, but I would like to create a function that uses a variable as an optional parameter: var = 2; f[a_:var] := {a} The ...
3
votes
3answers
193 views

Renaming a list with name obtained interactively

I have a list say: m = {1, 2, 3} The list is inside a package, and is the result of a calculation. I want to give the user the option to rename it, for example ...
1
vote
3answers
423 views

Adding subscripts to variables

I know I can define vars = Map[Subscript[x, #1] &, {"tem", "pressure", "hum", "lat", "alt", "space", "corner"}] and ...
5
votes
1answer
354 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. ...
9
votes
1answer
134 views
18
votes
3answers
740 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 $\mathrm{d}R$ for a function $R(a,b,c)$ ...
8
votes
2answers
240 views

Distribute and analyze large datasets

I need to analyze very large datasets, and they obviously don't fit in a computer memory. I need to produce some statistics on these datasets, and this brings me here: How can I make some statistical ...
8
votes
1answer
159 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] ...
4
votes
3answers
1k 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 ...