For questions relating to assignments to symbols, patterns, or expressions.

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5
votes
4answers
525 views

Is there any way to assign multiple values?

I am looking for something like "byref" assignment in programming languages. Let's assume I have: x1=x2=....=xn if I want to change their values ( say to 3 ) I need to set all of them like: ...
7
votes
2answers
633 views

Modifying parameters: Set::setps in the part assignment is not a symbol [duplicate]

Ok, this will probably be a silly question, but I can't get my head around it. I'm making a simple module that, given a list and two integers, will swap the position of the elements in the list.(...
7
votes
3answers
2k views

Assign output of solve to variables [duplicate]

I have this input: Solve[x^2 + 3 x + 2 == 0, x] which gives this output: {{x -> -2}, {x -> -1}} I want the first x ...
3
votes
0answers
121 views

Why is it not allowed to define vectors of variables in a scoping construct?

The following command assigns 1 to a, 2 to b and 3 to c: ...
-2
votes
1answer
218 views

Trouble to assign solution of differential equation to a function

I have written a function to Solve the following differential equation where the number n (called in my code Nphoton) is a variable. Nevertheless I have troubles to assign the solutions ...
1
vote
0answers
49 views

How do I assign a formula to a variab [duplicate]

I want to compute equations and assign them to variable. This is a wxMaxima program that calculated symbolic PID gains for an integrating first order system ...
3
votes
0answers
73 views

How to get Symbol[“x”]=3 to work [duplicate]

This is probably a really simple one, but I'm stumped. I want Symbol["x"]=3 to work just like x=3. However I can't figure out ...
5
votes
1answer
96 views

Edit built in symbol

I would like to add new attributes to built in symbols (e.g. ElementData or PolyhedraData) so that I can still call the symbol ...
8
votes
2answers
195 views

How to name a variable with the value of another variable?

A simple but very important (at least for me) question. In some languages for defining a variable, for example, we can do: i=10 "d"&i=30 So I have defined the variable d10, and... d10=30 ...
7
votes
3answers
370 views

Implementing key-value associations in Mathematica 9 with inexact numbers for keys

I'm not sure of what type of problem my issue falls into, so I haven't been able to search forums with any success. If this has already been solved then my apologies! Essentially I'm trying to set a ...
8
votes
1answer
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. ...
18
votes
4answers
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-...
3
votes
2answers
529 views

How to copy a function by value?

I need to change a function symbol multiple times by assigning another symbol to it, but when I'm trying to do that the symbols overwrite each other. I'm assuming this is because the assignment is by ...
0
votes
1answer
84 views

Questions regarding DictionaryLookup of Mathematica

a. Make a function longest[lang_] that gives the length of the longest word in the dictionary of lang. You should get ...
1
vote
2answers
162 views

Few quick Mathematica questions about Dictionary

a. Get the list whose elements are of the form {language,number of words in dictionary) I tried this, and it gave me the number if words in dictionary, but I don't know how to get the language part: ...
0
votes
3answers
150 views

Evaluating an expression assuming a value for a variable only in the local context

Imagine we wish to evaluate some expression like NIntegrate[x^2*q,{x,0,100}] assuming some value for q like ...
1
vote
0answers
62 views

Set-generating macro unexpectedly reaches recursion limit

One moment I decided to assign symbolic names to all special spaces since they all look the same when put literally in FrontEnd editor, more or less like "" or <...
1
vote
1answer
39 views

How to assign a list of subsript?

I want to assign Subscript[C,i] by mapping a specific list. For example, the list is {1,2,3,4}, and I want to assign 1 to C1, 2 to C2, 3 to C3 and 4 to C4. How should I do? Many thanks:)
2
votes
1answer
124 views

How to extract a variable names (not values) from a list of transformation rules?

I am trying to extract variable names from a list of transformation rules mapping = {var1 -> 'val1', var2 -> 'val2' }. Variables ...
3
votes
2answers
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 ...
3
votes
2answers
163 views

Unset while running recursion

I am trying to run a recursive definition while at the same time clearing previously found values, so my memory is not completely consumed. I found this: How to clear parts of a memoized function? ...
1
vote
1answer
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. ...
3
votes
1answer
74 views

Replacing multiple instances of a symbol with different variables and assignments

I have an expression of the form: expr=x+y+n+Sin[n]+n^2 I would like to replace each of the variables n with a different ...
0
votes
2answers
190 views

Associate the elements of a table

I have a table form as: table = {{a, 6}, {b, ff}, {c, 2}} I want to associate the first element of each pair from the table to the second element of the pair as ...
1
vote
1answer
72 views

storing rescaled images in new variables

I'm trying to assign random image files that undergo rescaling to a list of variable names. The images I'm trying to assign are the result of mapping the ImageResize function of two arguments to the ...
1
vote
1answer
144 views

Automatically assign solutions to equation as constants

Consider the following code: ...
6
votes
3answers
492 views

Understanding Function and Variable in Mathematica for beginner [closed]

I'm reading the book of Leonid Shifrin, and I love the way the book explains the core in Mathematica. As everything is an expression, now I understand that, there ...
3
votes
3answers
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 ...
0
votes
0answers
235 views

Assign variable's value programmatically [duplicate]

Not easy to explain what I'm looking for, so please sorry if I'm not so short. Having many variables to be managed in several different combinations, I need to automate the assignment of preset ...
2
votes
1answer
152 views

Assign one button to two variables

I am trying to use the one button to assign to two variables. Here is an example of how I want it to work. expression: ...
4
votes
1answer
1k views

Integral of Lorentzian yields different results depending on when parameter assigments are made

I'm evaluating the integral of a Lorentzian, which I know equals one. First I define the function and evaluate the integral in two slightly different ways. Surprisingly, I do not get the right answer ...
0
votes
1answer
361 views

Getting mesage: Set::setps assignment is not a symbol

Please, tell me what is the issue with the following code? Dimensions[Subscript[R, 2]] {201, 161, 53} ...
1
vote
1answer
190 views

Two quick Mathematica Questions about the dictionary

Question1: Get the list of pairs of the form {language,number of words in dictionary}. Call this list langlength What I did was this: ...
6
votes
1answer
1k views

Clear and Unset doesn't free memory

Example: Try this example only if you have > 4G ram d = 2000; f[x_, y_, d_] = Sum[Subscript[a, i, j]*x^i*y^j, {i, 0, d - 1}, {j, 0, d - i}]; Then ...
8
votes
2answers
322 views

How to ignore list elements when extracting with pattern matching

If I have a simple list, say {1, 2, 3}, and I want to extract a subset of the elements, what is the correct syntax? e.g. { i, _, j } = {1, 2, 3} I want i = 1 &...
24
votes
1answer
514 views

Why does list assignment with a packed array result in unpacked values?

Bug introduced in 5.2 or earlier and fixed in 10.1.0 This is another question on the design choices in Mathematica. I understand that without direct reply from the developers it may not be ...
0
votes
1answer
76 views

Extracting function variables from a list [duplicate]

Evaluating the following func[x_, y_] := x^2 + y^2 listn = {{a, b}, {c, d}, {e, f}}; Map[func[##] &, listn, {1}] yields {func[{a, b}], func[{c, d}], ...
4
votes
2answers
115 views

Choosing an initializer list in With

I'm trying to have several initializer lists in a With function and choose which one I want to use. So far I have this: ...
5
votes
1answer
338 views

Assign variables automatically to a function

Lets consider that I've this function: fn = a*x^2 + b*x + c; The idea here is to assign automatically the variables a, ...
8
votes
2answers
358 views

How to replace a variable that was assigned a value before

Question How to make the replacement $f[x] \to f[y]$ for an abitrary function $f$ if $x$ was assigned a value before? Example 1 How can I make the replacement $x +1 \to y + 1$ if I have assigned ...
8
votes
1answer
173 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] <...
9
votes
1answer
204 views

Unset variable by its name given as a string

Unlike the function Clear, the function Unset does not work for string patterns. Given the name of a variable as a string, how can you unset the corresponding variable? Example: Given: ...
1
vote
1answer
187 views

direct assignment to the element in a Table

I have already asked a related question here why set values in this way doesn't work? But I think I have to write the question which I encountered explicitly? ...
4
votes
2answers
219 views

why set values in this way doesn't work?

question is as follows define a list ttt={1,2}; and if I set values in this way {ttt[[1]],ttt[[2]]}={3,4} then the value ...
12
votes
1answer
434 views

Triggering actions when a variable is set

Some built-in variables trigger actions when their values are changed: ...
3
votes
3answers
121 views

Can I put subscripted parameter values into a package?

When defining packages, can I put parameter values alone or along with functions into a package in subscripted form? ...
1
vote
1answer
130 views

Using With in combination with Graphics [duplicate]

Assume that we are given a symbol p={x,y} which should represent a 2D point. If x and y have ...
1
vote
2answers
164 views

How to mix Unevaluated property of function arguments with expression assignments?

This is a follow-up to my (solved) question How to distribute a generic function of two arguments (without evaluating the arguments) Say, I have a binary function ...
14
votes
2answers
370 views

How to make use of NumericQ[x] = True (and use it safely)?

Basic Issue: I'm trying to understand the proper use of NumericQ's "magical" capabilities. Please consider the examples below. Actual question and some links are ...
22
votes
3answers
496 views

Nested definition: How can I define a function with a passed-in expression?

Here's a simplified version of what I'm trying to do: ...