Questions tagged [assignment]

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

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9
votes
4answers
495 views

Looping through 3 million elements of a list to 'Set' values is slow

I am looping through the 3 million elements of a time-series (v1, o1) and corresponding values (v2, o2). v1 contains a uniformly increasing timestamp (e.g. 1 to 3,000,000 in increments of 1) o1 ...
3
votes
1answer
117 views

Table generation with SetDelayed function [closed]

I would like to understand why the following two outputs differ: Let us define the following data set: ...
6
votes
2answers
233 views

Force evaluation of the right-hand side of a local variable definition

One can do expression = a + 1; f[a_] := Evaluate[expression] but how would one do something like this ...
0
votes
1answer
235 views

Correct definition of a function to be passed to Nintegrate [duplicate]

If I type the following code ...
5
votes
3answers
589 views

Turning an expression into a function inside another function

Say I have an expression g=Sin[q]; It is easy to turn it into a function, and to perform manipulations on this function (this and variants of this were discussed ...
1
vote
3answers
167 views

Setting ::usage for variables returned from a function

What is the best way to achieve {v,u} = f[]; (* Returns value and usage description *) v::usage = u; from inside f, i.e., <...
9
votes
2answers
290 views

Passing an unevaluated part of an association to a function

I'm making a UI widget that controls sound volume on a speaker using a slider, e.g.: ...
0
votes
1answer
322 views

Variable dependency…easy one

I'm brand new to Mathematica...should be an easy one. Instead of writing u[x] everywhere in the code, how do I assign the dependency early on like this: u=u[x] ...
4
votes
2answers
135 views

Initializing several values of a function

How do I initialize several values of a function at once? Consider the function f[0] := 1; f[1] := 2; f[2] := 3; f[n_] := f[n] = f[n-1] + f[n-2] + f[n-3]; Is ...
4
votes
2answers
588 views

Assignments in ParallelDo when using indexed variables

For convenience I use an indexed variables syntax to hold results of long computations for different integer parameters: ...
8
votes
1answer
840 views

How is LHS = RHS; … ; LHS (nontrivially) different from … ; RHS

I'm trying to understand how Mathematica thinks about the results of Set. Suppose we perform LHS = RHS. I'm focusing on when ...
3
votes
0answers
41 views

Out[x] not the same as assigned expression [duplicate]

There seems to be a difference in the way Mathematica assigns a value to a variable and the way it assigns a value to the next Out object. I don't understand why this is happening. For instance, take ...
3
votes
1answer
775 views

Is there a way to simplify a symbolic expression at assignment, once-for-all?

I have a series of symbolic function calls that could be greatly simplified using some assumptions. I think I would like for these assumptions to be used in the definition of the function so that they ...
1
vote
1answer
132 views

Is it possible to assign a value where the target is itself a variable

If I have a variable x := "a". Is there a way I can use it to assign a value to a, by just referring to ...
7
votes
2answers
198 views

Problem with Simplify, Sqrt, and Set: What's going on?

I am having some trouble getting Mathematica to simplify an expression of the form Sqrt[x]*Sqrt[1/x], where x>0. The problem ...
4
votes
3answers
382 views

Using Block with a list of variables

I have a list of variables var={v1,v2}; which I want to protect/localize during a particular operation. I have decided that I want to use ...
1
vote
0answers
28 views

Assign to variables inside Array, rather than changing array entries [duplicate]

I am generating an Array with symbolic coefficients: coefficients = Array[c, 3] > {c[1], c[2], c[3]} I would like to assign a value to each of these generated ...
0
votes
2answers
525 views

How to assign the values for the Table list?

Now, I want to assign some values for a Table list and I find that If {mat[1], mat[2], mat[3], mat[4], mat[5]}={4,23,3,12,1}; it is no problem. But, if we use ...
13
votes
1answer
258 views

Why can AppendTo modify a referenced list in-place but Part cannot?

Part, AppendTo, PrependTo, AddTo, etc. allow in-place modification of a list, but only Part requires that the list be referenced through a simple symbol, e.g. the following all does what you'ld expect:...
1
vote
1answer
130 views

Simultaneous use of Set AND SetDelayed

Tha Mathematica documentation gives a good example of the simultaneous use of Set and SetDelayed in dynamic programming for the Fibonacci sequence under "neat examples" for SetDelayed ...
0
votes
1answer
85 views

Refercing generic derivatives

I have a list of rules to the values of the derivatives of a generic (real valued, 3 variables) function, for example: df/dxdydz(0,0,0)-> 0.7. I would like to be able to generically reference this ...
1
vote
2answers
111 views

Assigning to the “local” version of a symbol

Compare Manipulate[c[1] = 1; c[1], {c[1], 0, 1}] with Manipulate[Do[c[i] = 1, {i, 1}]; c[1], {c[1], 0, 1}] The first case ...
4
votes
3answers
610 views

Altering values in Manipulate with dynamically generated controls

I have a Manipulate whose controls are generated based on a parameter in a containing Manipulate: ...
9
votes
2answers
173 views

DownValue assignment using Apply

Why does assigning a DownValue using Apply, e.g., ...
29
votes
3answers
533 views

Assign a randomly generated list to variable

Bug introduced in 10.0.0 and fixed in 10.0.2 I don't know if this is a silly question, but it really baffles me. So please help me understand this behavior. ...
6
votes
4answers
1k 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: ...
9
votes
2answers
3k 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.(...
12
votes
3answers
8k 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 ...
4
votes
0answers
214 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
465 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
52 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 ...
4
votes
0answers
104 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
115 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 ...
9
votes
2answers
532 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 ...
49
votes
3answers
4k views

Changing Values in an Association using Map

I am trying to change the value of one key in an association based on the value of another key in that association. So if my association starts as: ...
7
votes
3answers
501 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
126 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. ...
20
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
764 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
106 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
186 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
188 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
67 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
46 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
180 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
255 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 ...
4
votes
2answers
218 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? ...
10
votes
6answers
870 views

Generate list of strings from a list of assigned variables

How do I generate a list of strings from a list of assigned variables? E.g. convert ...
1
vote
1answer
109 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
95 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 ...