# Tagged Questions

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.

196 views

### Identifying the symbol which has a specific value

I'm writing a program that will solve the value of 1 variable in a 4-variable equality equation, but the variable to be solved will depend on the user's input to the program. This is what I've come ...
82 views

### Calling variables with use of numbers in their names

I have got few huge matrices named by ascending numbers, e.g. x1, x2, x3,... and I need to do the same operation with all of them - to multiply their components, ...
129 views

### Extract memoized results in the form of a rule

Lets say I define a function f with memoization. Is there some way to extract the memoized values? For example, ...
376 views

### Define function that counts recursive fibonacci

If I write count=0; fib[0]:=(count=count+1; 0); fib[1]:=(count=count+1; 1); fib[n_] := (count = count+1; fib[n-2] + fib[n-1]); Then I can ...
48 views

### Indexed variable with alternatives

I have a["tree"] := "oak" a["flower"] := "rose" a["dog" | "cat"] := "animals" I want that the last definition of a behaves ...
77 views

### How I can define a new function as a function argument?

I need to pass a function with t as independent variable as a function parameter and want to create a new function of the same through this provided the argument of another function. Here is my code. ...
39 views

### Can the value of a variable be made to persist between front end sessions? [duplicate]

For example, say I create a notebook with a cell a = 5 + 2 and then I close Mathematica, reopen the notebook, enter a new cell ...
97 views

### How to localize symbols on the right-hand side of Rule when using ReplaceAll? [duplicate]

I am frustrated by the following: {1, 2, 3.0} /. a_Integer -> a + 1 The a on the left side of the arrow is localized and ...
203 views

### When to use indexed variables

Still learning the fundamentals of the language I would like to ask you what advantages there might be in writing something like: a[1] = 2; a[2] = 4; a[3] = "x"; ...
62 views

### Quoting definition explicitly

I'm trying to quote a definition using DownValues, OwnValues, etc. Everything seems to be fine, except for temporary symbols' ...
55 views

### Get value for a variable from user inside a module [duplicate]

I am writing a module. When I run the module, I want it to ask for a variable, like I can in other programing languages such as C++ or Python. For example, in C++: ...
118 views

### Maximum number of literal values for SetDelayed?

Under what circumstances should I expect Mathematica to turn a delayed assignment into an immediate assignment? I have put together a minimal example (available here) which demonstrates this behavior. ...
139 views

### Using a variable for two different purposes

I want to name a bunch of tables after the OEIS entries which describe them. Is there any way to use these names for both the table name and the link at the same time? The second line uses the ...
312 views

### Treat strings as variables?

I have a list of strings, {"x1", "x2", "x3", "x4"} And a list of linear equations: ...
2k views

### How to implement the Observer design pattern?

As a programmer with a history with procedural languages, the Observer design pattern inmediately springs to my mind when attacking certain class of problems, mostly UI/notifications related. A two-...
879 views

### How to define a matrix with all elements 0? [closed]

A matrix can be defined as M = Array[m, {3, 3}] which gives ...
36 views

### How to change $n$ variables with $n$ Buttons automatically [duplicate]

I was trying to make a little game, and I came accross this problem. The goal is simple. There are going to be $n$ number of buttons, and each one will change a value of one variable. For example, ...
58 views

### How to set the values into some variables from different lists [duplicate]

I have a list of Values and a list of variables. I want to set the Values into Variables. Assume the following code: ...
184 views

### Clean-up Code / Reduce variables

I'm writing a playing card simulator of sorts, and everything works fine, but some Modules use a disgusting amount of variables. For Example: ...
68 views

### Block, With, Module, can anyone help me understand the distinction? [duplicate]

I've been working heavily with Block[] for months in my research so I've read the documentation for the seemingly similar commands With[], Block[], and Module[]. Personally, I've had by far the ...
61 views

### Telling mathematica that something is an integer [duplicate]

Is it possible for me to tell mathematica something is an integer? like if I typed Sin[n Pi]+Cos[n Pi] it would tell me it equals 1 for even n and -1 for odd n? ...
286 views

### Defining my own invisible operator

There are some invisible operators in Mathematica (\[ImplicitPlus],\[InvisibleTimes],...
226 views

### setting real parameters in Hamiltonian matrix

The following Matrix represents my Hamiltonian. m = {{ B/2 - d - j/2 + a, (Sqrt[2]*j)/2, M}, {(Sqrt[2]*j)/2, B/2 + a, 0}, {M, 0, (-3*B)/2 - d + j/2 + a} How can ...
168 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 ...
564 views

### How to take derivative of parameterized coordinate?

Suppose I have a vector in $\mathbb{R}^n$ but $n$ is not known in advance. I want to be able to write functions which operate on the components of that vector, and then I'd like to be able to take ...
294 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 ...
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) ...
252 views

Hello, ...
95 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. ...
320 views

### Another difference between Set and Setdelayed. Evaluation shortcut?

A little while ago I wondered why f[x_] = f[x] gives an infinite iteration. I ended up discovering the following difference in evaluation between ...
255 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 ...
203 views

### How can I define a âŠ• operator?

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

### Why x = x doesn't cause an infinite loop, but f[x_] := f[x] does?

If I execute: In[1] := x = x Out[1] = x and then I evaluate the symbol x: ...
206 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 ...
363 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 ...
412 views

### If statement condition based on variable without value does not cause error

This code works as expected: ...
1k 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 ...
271 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 ...
199 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 ...
140 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 ...
178 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 <...
102 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 ...
1k 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 ...
101 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: ...
637 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 ...
308 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 ...
3k 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 ...
189 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 ...
1k views

### Preventing Superscript from being interpreted as Power when using Ctrl+^ shortcut?

I have very strong desire to use superscript as the index of the variable. However, it looks like that the Mathematica automatically recognize the superscript as the power and I got message that my ...
140 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 ...