Questions tagged [variable]

Questions on the use or manipulation of Mathematica variables (i.e. names associated with a changeable value). Use [variable-definitions] or [assignment] for questions on variable context localization, or assignment.

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1answer
32 views

remove one of the column in the output of Solve command

I would like to remove one variable in the output of the "Solve" command without changing the rest. For instance, in the following code ...
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2answers
77 views

From f[g[x,t]] to f[g]

How can you change f[g[x,t],t] to f[g,t] ? I have differential equations ...
4
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1answer
30 views

Computing Higher Order Tensor of Variable Rank

The following code takes a vector x of variable length, computes the outer product of the vector with itself to form the matrix $\rho$ of dimension $2^n \times 2^n$....
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1answer
34 views

Functions with Variable Numbers of Arguments: Outer Vector Product

I am trying to write a function that takes a column vector of variable dimension as an input and returns the outer product matrix as an output. What I have tried: ...
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3answers
441 views

How to transform a function from f[#1] to f[x]

So I have this function : Sqrt[-1 + Tanh[#1 - #2]^2] & How can I transform it into f[x_,y_]=Sqrt[-1 + Tanh[x - y]^2] ...
3
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1answer
410 views

General::ivar 0 is not a valid variable when using Series in Plot

I have been having some trouble graphing a Taylor series approximation (Series). ...
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1answer
73 views

Make assumption for function with variable argument

I would like to assume that a>t[b_] for any b, such that e.g. Simplify[a>t[c]]==True. ...
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0answers
28 views

Saving variable inside Manipulate command

I have been working in a plotter using "manipulate", I let the code below. However, I would like change between different kind of "options" that I will add them after, the problem is when I change to ...
2
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1answer
68 views

How to read in and assign values from a txt file?

I have a text file that I would like to import into Mathematica - after searching around the internet, I can't seem to find any pages that explain how to do this: The text file containes these four ...
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1answer
57 views

Table and FindRoot of a 2 variable function of x and t : cos(x + 3t)

I am trying implement mathematica commands: Table and FindRoot, of a 2 variable function <...
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0answers
82 views

Problem with fitting

So I have a very simple question related to a simple topic, but also directly related to a fitting problem. I see that my question is related to this question but I don't manage to make the bridge ...
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2answers
49 views
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1answer
58 views

Five equations to solve 6-variables question, is it possible?

I was given a task to find the value of variable a,b,c,d,e and f. But I'm not sure it is even possible, given that only 5 equations are available. Can anybody point out how to solve these: ...
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1answer
35 views

How to use a table with two variables as the values for a function with two variables (x and y)? [duplicate]

I'm sorry if this is a dumb question. I am a student and have 0 prior experience with Mathematica or any sort of coding and I have looked at various resources trying to figure it out myself but still ...
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0answers
31 views

Bounding Solve results to named variables

How can i bound results of my Solve function to variables properly? This metod works but causes unexpected troubles i struggle to resolve ...
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1answer
128 views

How do I create a variable that uses I?

I'm planning on working with a set of non-linear differential equations. A few of the equations look like: Mathematica tells me that I is protected. Is there any ...
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3answers
34 views

Simple question about variables into functions

Im trying to write a very simple code that will solve an equation. total = 800; side1 = x; side2 = total - 2 x; f[x_] := side1*side2 f[x] f'[x] Solve[f'[x]==0] ...
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1answer
22 views

How to define a function, that generates matrix of variables, which can be later used in Reduce?

My goal is to generate matrices, on which I will put different constraints in Reduce funcion, e.g.: ...
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2answers
69 views

Separating variables in a set of equations

I have a very large set of equations eqs with variables denoted by capital letters like PVA[2], QA[2], etc. and small letters like ica[1,2], tr[2,3] etc. And I have ...
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1answer
46 views

Apply different PlotStyles to functions with functions as variable [closed]

I have a function func[expr,var] with which I want to plot the list expr[var] and have different styles applied to it. When ...
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1answer
46 views

Rearranging similar terms in an equation

In a piece of code I am writing, I run into an equation of the form ...
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2answers
52 views

How to show the answer in terms of another variable

if we have A = 1; B = 44 + 1 output :: B = 45 how we can show B like this output :: B = 44 + A
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1answer
46 views

Changing variables to obtain derivatives of new variables [duplicate]

Let's say that I have some symbolic expression of a function $x(t)$, and would like to obtain its derivative $x'(t)$. However, I also have the following two identities, $\xi = \omega t$, and $\eta = ...
4
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1answer
248 views

Why is DSolve different when the equation is built programmatically?

Here is a simple differential equation. mwe=y[x]/.First@DSolve [{y'[x]==x-2*x*y[x],y[0]==0},y[x],x] I get the answer $\frac{1}{2}-\frac{e^{-x^2}}{2}$ If I build ...
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1answer
56 views

Why is ww[[1]] not a valid variable in FindMinValue and Plot [closed]

Why is ww[[1]] not a valid variable when given to FindMinValue and Plot, but is a variable ...
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0answers
27 views

How can I access the name of a variable inside a function? [duplicate]

How can I access the name of a variable inside a function? For example I have variables mike={some stuff} jenny={other stuff} and want to write a function f giving the following: input> f[mike] ...
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1answer
130 views

Can I bake my own PI using your Wolfram language oven and prebuilt utensils? [closed]

How might I override the value of the Greek letter PI within various builtin language functions in the Wolfram language? Specifically and without having to reinvent the wheel or code equivalent ...
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1answer
75 views

Computing an integral : Mathematica seems to say it's diverging or not defined and I think it is

I would like to compute : Element[a, Integers] Element[b, Integers] Integrate[Exp[-a^2*(x (1 - x/b^2))^2], {x, 0, Infinity}] which is obviously not diverging. ...
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1answer
39 views

Inequality with assumptions

I would like to find 2D region formed by $(a,c) \in \mathbb{R}^2$ such that the inequality $f(a,c,x,y) \geq 0$ holds for all $x,y \in [0,1]$. If I solve this inequality with reduce of the form ...
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1answer
37 views

Factoring out a parameter

I have some function: f[a_,b_,c_]:=Sqrt[a^2+b^2+c^2] Is there a way that I can factor out parameter (variable) b like this: <...
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1answer
90 views

What is the recommended way to plot a function with a dependent variable?

I am currently learning the basics of Mathematica. I can't seem to find a straightforward answer in the Wolfram documentation, probably for a lack of clarity in my queries. For example, I want to ...
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1answer
43 views

Question about ListPlot of variables [closed]

My question is trivial but I don't seem to be able to get the answer. Suppose that I do a numerical computation (division of some numbers that come from the numerical solution of an NDSolve or ...
3
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2answers
61 views

Using Symbolize to Convert Multiple Variables at Once

So, I have created a list of subscripted and overdotted variables that I would like to symbolize, so I run them through a for loop. Seems to me that this would work? Any help is appreciated. ...
6
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0answers
63 views

Nested rules and automatic renaming of variables [duplicate]

I understand why $ happens here: ClearAll[foo] foo[a_] := (x_ :> a x) foo[1] ...
2
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2answers
93 views

Possible to solve this function?

I have this function: Emax[T_, d_] := -(1/2) + d + d/(-1 + E^(d/T)) - 1/2 Coth[1/(2 T)]; All I want is to transform this Function so I get: ...
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2answers
56 views

Showing variable values on a 3D Plot

I am running a 3D plot a 100 times to show the dynamics of two undetermined variables (cM and cR) for a 100 values of ...
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1answer
26 views

Extract and name PNG's from loops [duplicate]

I want to extract PNG files and name them depending on the dummy variable of a loop. For example, starting from ...
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1answer
38 views

Use Solve for two Functions to find 1 common Variable

I have 2 functions that look like this: F[t_,d_]:= 10+t+2d G[t_,d_]:= 5+t+d I'd like to solve this in such a way to know for which t both Function have the Same value. I assume that this won't be ...
17
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2answers
325 views

When to name a variable with $

There are some symbols in the Wolfram Language that start with $, including $Abort, ...
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1answer
51 views

Mathematica is picking up variable definition from other files

Mathematica is using definitions from other open files in the same folder. I want variables not defined in a particular file to be treated as undefined variables. I do not want Mathematica to pick ...
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0answers
29 views

Problem in importing function in NDSolveValue

I have a code for solving a system of 2 differential equations (sol1). Given that what's inside is a bit heavy, I define functions so that I can call them. My issue is that when I write everything ...
2
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2answers
112 views

Define a function of a function of an arbitrary variable

I want to define a function called int that takes another function as an argument and yields an integral of that function from 0 to 1 (just for example). So I ...
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1answer
46 views

Plot interpolating function depending on free variable inside manipulate

I create an interpolating function which depends on some free variables. I then want to plot it inside a manipulate, but my output is empty. What am I doing wrong? ...
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1answer
35 views

Altering the Values of Global Lists Within Tables

Say I have some lists: list1 = {4} list2 = {2} list3 = {6} list4 = {9} list5 = {7}. I want to alter them in a table like so: ...
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1answer
73 views

Solve an equation with two specific domains?

In Solve an equation with specific domain? I asked how to write a code in Mathematica with one specific domain for one of its variables. Now I have a questions: If two of the variables are from ...
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2answers
302 views

Solve an equation with specific domain?

How can I write a code in Mathematica to solve an equation with variable in specific domains? For instance, I want to write a code for ...
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2answers
147 views

How to replace Variable With Variable [closed]

Clear[a, b, c]; a = c; a =. ; b = a; b =.; c = b; c =.; Print[a, b] and the result is {a b} but I want the result ...
0
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1answer
77 views

Automatic variable naming

I am trying to construct a complicated code in which I need to name a lot of variables and their definitions. For Example: The problem is as follow: Once I insert new variable in between two, I ...
1
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1answer
49 views

Using Variables[] as the argument of Plot[]

I want to use the Variables[] function to extract the name of the variable of a function, such that I can use it later, e.g. in a ...
0
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1answer
61 views

How to plot solutions for simultaneous equations

I have 2 simultaneous equation of $x$ and $y$. Here is how I solve it, and it works. But I want to vary the parameters n and ...