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

learn more… | top users | synonyms

6
votes
3answers
387 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
131 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
198 views

Assign variable's value programmatically

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
138 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
824 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
239 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
143 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: ...
8
votes
2answers
234 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 ...
0
votes
0answers
184 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: ...
20
votes
5answers
591 views

Reassign values to symbols

I've got a situation where I have, say 4 symbols, a, b, c and ...
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 ...
5
votes
1answer
280 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
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
168 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
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
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 ...
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 ...
10
votes
3answers
344 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 ...
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
347 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 ...
4
votes
2answers
829 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 ...
10
votes
2answers
792 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
155 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 ...
7
votes
1answer
319 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 ...
11
votes
3answers
374 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 ...
15
votes
1answer
275 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 ...
16
votes
2answers
209 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) ...
113
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
895 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 ...