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

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7
votes
2answers
281 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
160 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
165 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
206 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
371 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
122 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
153 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
344 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
406 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
816 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
191 views

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

My code: ...
18
votes
5answers
15k 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
773 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
154 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
482 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 (...
30
votes
1answer
633 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
95 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
313 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
507 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
316 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
372 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
342 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
332 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
274 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
158 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
814 views

How do you set attributes on SubValues?

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

Reassign values to symbols

I've got a situation where I have, say 4 symbols, a, b, c and ...
110
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
888 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 ...
15
votes
2answers
208 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) ...