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

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0
votes
2answers
42 views

Can you unpack a list of values into variables in a With expression?

For instance, if I am trying to draw a graph with 5 vertices labeled a through e, and I want to draw edges connecting a and b, a and c, a and d, a and e, b and c, b and d, and c and e, I would run the ...
0
votes
1answer
43 views

How to use Set correctly

My codes are shown in the picture attached. I'm writing codes for numerical calculations frequently, and I think it looks neat and clear to organize input parameters in the form of table. For example,...
4
votes
1answer
78 views

Using delayed evaluation on module variables called through an association

I came up with a construct that works well enough for my current use case but has some flaws (at least I suspect it does). Say we have a function that calculates some stuff that takes a while to ...
0
votes
0answers
38 views

Create a loop for assignment of Solve output [duplicate]

Is there a way to automatically assign the output of solve to a number of symbols? For example, assume that I have the solve statement as follows: ...
8
votes
2answers
69 views

How do I SetDelayed $Assumptions

For some reason, $Assumptions := (Print["y"]; x > 0) evaluates the RHS immediately. I have code in which $Assumptions ...
0
votes
0answers
21 views

How to make an expression in this case evaluated one step and stop there? [duplicate]

I wonder how to make Symbol@"m" evaluated once so that it becomes a symbol m which is ready to be assigned again. ...
1
vote
1answer
62 views

How to assign options to a variable?

I want to redefine a function similar to Plot like this: ...
2
votes
2answers
86 views
-1
votes
1answer
53 views

Iterate a large matrix calculation [closed]

I want to repeat the calculation of a pretty big formula about 100 times. I tried using Do loop but it takes sooo much time that mathematica stops working. I will take a simple example to illustrate ...
2
votes
1answer
54 views

How to determine where a variable got assigned a value?

I have a Mathematica notebook that includes some dynamic structures (with Manipulate). Sometimes, I discover that x has been ...
9
votes
0answers
67 views

Is there a way to TagSet a HoldAllComplete function?

Let's say I want to overload the built-in function Lookup, to handle my data wrapped in myObject. One would use ...
1
vote
1answer
119 views

Is there any way to implement a “sequential” With[] in Mathematica? [duplicate]

I want the equivalent of Scheme's let*, or basically, a sequential With that works like this: ...
10
votes
6answers
619 views

How do I randomly divide individuals into groups?

I would like to assign 'x' individuals to 'y' groups, randomly. For example, I would like to divide 50 individuals into 100 groups randomly. Of course, with more groups than individuals many of the ...
0
votes
1answer
37 views

Where is the erroneous assignment that is causing my 'List of equations expected instead of tru' error?

I'm getting one those annoying 'NDSolve::deqn: List of equations is expected instead of True' errors. I have done everything I can think of to Remove and Clear all variables, including restarting ...
4
votes
2answers
78 views

Append fixed value to random selection of list

(This question might be an application of this other question, but there might be another solution specific to this application that I'm not aware of.) I am currently in a situation in which (in a <...
2
votes
1answer
66 views

Writing my own error and warning messages

Question: How is message handling implemented in Mathematica when applying Set to unprotected global variables such as $TimeZone...
0
votes
0answers
26 views

delayed assignment (:=) vs assignment (=) difference example [duplicate]

After reading through the documentation, I still do not understand the difference between delayed assignment (:=) vs assignment (=)? Can you give me some easy and simple examples? I am not very good ...
10
votes
3answers
188 views

Why is the first argument of the SetDelayed evaluated?

In[1]: f=g; In[2]: SetDelayed[f[x_],x^2]; In[3]: ?f Global`f f=g In[4]: ?g Global`g g[x_]:=x^2 However, SetDelayed has the ...
9
votes
4answers
414 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
77 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
119 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
61 views
5
votes
3answers
231 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
125 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
167 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
119 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
131 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
155 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: ...
7
votes
1answer
311 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
38 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 ...
2
votes
1answer
277 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
78 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 ...
4
votes
1answer
96 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 is that x is assigned to some complicated form by the time Mathematica ...
4
votes
3answers
241 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
24 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
67 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
214 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
94 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
62 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
90 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
337 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
138 views

DownValue assignment using Apply

Why does assigning a DownValue using Apply, e.g., ...
28
votes
3answers
440 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. ...
5
votes
4answers
512 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
603 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.(...
6
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
120 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
213 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
72 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 ...