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

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8
votes
2answers
238 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 ...
22
votes
1answer
468 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
0answers
186 views

Assigning numerical values to constants results in complex coefficients in Equations of Motion

I am using Mathematica to get the Equations of Motion (EOM) for a mechanical system (using Lagrangian Mechanics). While I get the EOM in symbolic form, on introducing the following code for assigning ...
0
votes
1answer
71 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
285 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
297 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
161 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] ...
1
vote
1answer
169 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
209 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 ...
11
votes
1answer
373 views

Triggering actions when a variable is set

Some built-in variables trigger actions when their values are changed: ...
3
votes
3answers
115 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
123 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
154 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
350 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 ...
20
votes
3answers
411 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: ...
4
votes
2answers
845 views

How to store value in a For loop

I am using two For loops. When the inner loop finishes, I don't want to print but I want to store the result from the inner loop in some variable so that I can call ...
7
votes
1answer
192 views

Is this a good way to assign a Solve result to a function?

My code: ...
19
votes
5answers
16k views

Assign the results from a Solve to variable(s)

I understand Mathematica can't assign the results of a Solve to the unknowns because there may be more than 1 solution. How can I assign the 4 values of following result to variables?
10
votes
2answers
825 views

Scoping in assigning a derivative

While answering another question, I stumbled upon a problem I cannot easily resolve. To assign the derivative of a function to another function, typically one can do this with a ...
3
votes
1answer
156 views

Set promotes Rule to RuleDelayed?

In mentally building a model of how Mathematica works, I naively expected Set to create a Rule in a symbol's ...
17
votes
2answers
501 views

Does Set vs. SetDelayed have any effect after the definition was done?

I was always assuming that the only difference between Set (=) and SetDelayed (...
32
votes
1answer
648 views

How to augment the realm of functions Mathematica thinks it knows how to integrate symbolically

My question involves extending the functionality of Integrate over specific integrals in the most generic manner. Specifically, is it possible to "hack into" ...
3
votes
1answer
96 views

Syntax Coloring for “Possible Unwanted Assignment” Issue

Apparently Mathematica's syntax coloring engine believes that the second assignment in the following code excerpt (concocted for illustration purposes only) is a "Possible Unwanted Assignment" since ...
7
votes
1answer
323 views

Assignment rule to distribute matrix-multiplication over custom notation

I'm trying to write some code to do basic algebraic manipulations in BraKet notation. Thus far I have a function KetToVec which will convert any expression of the form a1 Ket[s1]+ b Ket[s2] +... to a ...
8
votes
3answers
3k views

Assigning values to a list of variable names

As part of a calculation I need to do something like this Evaluate[{aaa, bbb, ccc}[[ index]]] = {1, 2, 3, 4, 5} so if index is ...
5
votes
4answers
539 views

Delayed evaluation of assignment

I have a set of PDE's that depend on parameters. They depend on many parameters, but for simplicity we can here assume that they depend only on one, say a. I want ...
17
votes
4answers
317 views

Setting parts of a list

Suppose I have list a = Range[10] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} in which I want to set some elements to be a list ...
11
votes
3answers
376 views

MapThread gives different results from ToExpression when trying to assign variables from a list

I have the following data set: data = {{"Jakarta","Surabaya","Bandung"},{1,2,3}} and I'd actually like to assign the numerical values to the categorical data so ...
19
votes
5answers
2k views

How to pass a symbol name to a function with any of the Hold attributes?

Given a function with the attribute HoldFirst, HoldAll or similar, and a variable, list, how ...
10
votes
3answers
346 views

Why does ++++x return an increment of 2 when the value of x is only incremented by 1?

This line returns 3: x = 1; ++++x However, the value of x after the increment is only ...
8
votes
3answers
339 views

How to write a function-defining function which stores the function arguments in a stack?

I have a function-defining function SetAttributes[DefFn, HoldAll]; DefFn[f_[args___], body_] := f[args] := body; I am trying to modify this function to record ...
15
votes
1answer
281 views

How to make a function like Set, but with a Block construct for the pattern names

How can we define a function that works like f[x_]=ComputeSomething[x] and treats x as a variable that does not have a value? ...
1
vote
1answer
159 views

Differentiation w/o assiging concrete values

v = Subscript[v, 0]*Sin[(Pi*S)/Subscript[S, 0]]; a = dv/ds v; a = D[v, s] returns ...
26
votes
1answer
835 views

How do you set attributes on SubValues?

SubValues, as discussed in a previous question, are declared as follows ...
20
votes
5answers
598 views

Reassign values to symbols

I've got a situation where I have, say 4 symbols, a, b, c and ...
115
votes
2answers
5k views

What is the distinction between DownValues, UpValues, SubValues, and OwnValues?

When reading through the documentation, you often encounter the phrases DownValues, UpValues, ...
18
votes
4answers
899 views

How can I randomly generate a unique, unused symbol?

In a previous question on collecting terms for a multivariable polynomial, I answered with a solution that required a unused symbol to be used for a temporary substitution and back substitution. It ...
16
votes
2answers
211 views

Clearing a specific definition

Consider the case where a symbol has multiple definitions attached to it, a /: Subscript[a,2] := 1 a[b_] := 2 a[b_, c_] := 3 How does one clear (/unset/remove) ...