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.
252
questions
0
votes
0answers
33 views
Assign Variable to NSolve
I'm looking to create an interactive region plot in Mathematica, and it's quite a complicated region (seen below).. The variable p is actually a function of y, and it's too hard to solve analytically. ...
0
votes
0answers
29 views
Replace the output of a module containing local variables by their actual value
I want to construct a function as the output of a Module, but I obtain the local variables as part of the output. This is a problem when I try to construct many of these functions in a parallel table, ...
0
votes
2answers
56 views
Solving equation for unknown and replacing it in second equation
I am new to Mathematica and struggling with its syntax.
I have a set of equations, which I would like to solve for my unknowns.
I would like to solve the first equation for the first unknown and ...
0
votes
0answers
76 views
Issue with several replacements in a function under certain conditions
I am trying to define a function (reduce[x]) which does several substitutions, depending on the values of certain parameters. Concretely, consider an expression x, which contains an arbitrary number ...
1
vote
1answer
159 views
Desktop vs. Cloud option, home plan vs. basic plan: syntax differences
I do not understand why the following simple expression is accepted using a browser (cloud option), but is not accepted using the installed software (desktop option) with the plan basic of Wolfram ...
1
vote
1answer
62 views
How to do importance sampling to estimate variance?
For a random variable X with density $q(x)=e^{(1/3)∗|x|^3}$, I can estimate its variance by numerical integration method.
Then, how can I do importance sampling using a standard normal proposal (...
2
votes
1answer
45 views
Extension of Coefficient to variable exponents
Say I have an expression that is a polynomial in a variable, for example in the variable $x$, in which terms appear for which the exponent of $x$ also includes variables. For example:
...
1
vote
0answers
51 views
Mathematica says that a variable is not defined, yet it gives me a value [duplicate]
this is probably a dumb question (Mathematica noob here) but I can't figure out what's going on. I have a variable that I assign a value to and use, then later in the notebook I assign it a different ...
2
votes
1answer
53 views
Why some variables get substituted and others don't
I was running into some trouble with my math and I whittled it down to this nugget:
...
4
votes
1answer
82 views
Use a variable to represent another variable?
I'm trying to create a list of functions by replacing variables in a template. I tried this:
...
1
vote
1answer
81 views
how to define an example of ODE that represents an undamped forced oscillator whose time evolution is described by beats
I am a newbie in Mathematica and I really don't know how to define an example of ODE that represents an undamped forced oscillator
0
votes
1answer
54 views
Changing the dependent variable
I'm using NDSolve to solve a set of ordinary differential equations.
The output is something like.
...
0
votes
0answers
31 views
No Solution For Solve with Free Variable [duplicate]
Mathematica returns no solutions for this simple query:
Solve[a*x == x && x != 0, {x}]
(* output: {} *)
Clearly, when a ...
0
votes
1answer
62 views
How to asign well numerical values efficiently before to plot?
A problem is presented when the substitution of the numerical values for this function
...
2
votes
0answers
48 views
Issue with calling one notebook from inside another one
I am calling one notebook (N2) from inside another notebook (N1). The results are transferred correctly from the second notebook to the first one. But when I try to compare the results from the two ...
2
votes
1answer
38 views
How to Append the value of a variable and not the variable itself
So lets say I have
a = Some complicated code that changes
list = {}
AppendTo[list, a]
Obviously it would give me
...
0
votes
0answers
66 views
Using an if statement to assign a value to a variable
New Mathematica user here. I'm using some code from a colleague and editing it to give me more specific results in finding the zeros of a complex polynomial. I am attempting to find a way to assign a ...
3
votes
2answers
65 views
Better way for constant expressions in functions than storing as global variables?
For example, I wrote a function like this:
inversions[list_] := Complement[
Subsets[{1, 2, 3, 8, 4, 7, 6, 5}, {2}],
Subsets[list, {2}]
]
But as you see, ...
1
vote
1answer
203 views
How to obtain non-trivial solution?
I have the following system of equations.
$ quad\quad\quad\quad u+\alpha v+v+e^{\frac{i \alpha }{2}} (\alpha -1) x=\alpha u+e^{-\frac{1}{2} (i \alpha )} (\alpha +1) z, +u+v=\alpha (v+w)+w+y, (\...
4
votes
1answer
50 views
Name of patterns cast as expressions from strings
I'm trying to match a part of a string while imposing conditions on the patterns, e.g.:
StringCases["223", a: DigitCharacter ~~ b: DigitCharacter /; Unequal[a, b]]
...
0
votes
2answers
75 views
Integration result depending on variable name
From previous threads I have read on the subject, it seems that Mathematica is known to simplify expressions to varying degrees depending on alphabetical order of chosen variable names. But none of ...
1
vote
0answers
35 views
How to return a variable name and value from within a self-contained function block?
Abstract: I have viewed other solutions on StackExchange but none actually address using a fully self-contained function to return name and value of a variable. The only function that works requires ...
1
vote
2answers
75 views
Getting the name of a variable instead of its value [duplicate]
I want to get the name of a variable instead of its value in output. Say I have a function in which I have vectors
e={1,0,0,1} and ...
3
votes
1answer
85 views
Again about Module inside other Module
Let me start with a short preamble.
I have a large function (defined through other functions) which I need to integrate numerically. This works.
Trying to speed up the process, I played with ...
0
votes
0answers
23 views
How to retrieve variables in the Manipulate's 'dynamic' controller environment
I'm trying to code to generate 'dynamic' controllers and to set initial values (initStart and initEnd):
...
6
votes
4answers
202 views
Assigning a string to variables names
I have the list
n1 = {{REL1, "REL.csv"}, {RAND1, "RAND.csv\"}}.
That is {{variable name, string}, {name, string}}. I want ...
0
votes
1answer
43 views
Assign variable to solve [duplicate]
I would like to assign my result from equation. I tried /. and := but it gives me empty variable. How can i fix it?
2
votes
1answer
41 views
Problem with superscript
I would like to know if there is option to make such scrpits like in this picture below.
Is option to put letter instead of a *?
0
votes
0answers
4 views
Assigning a solution to variables [duplicate]
I have solved my solution and it has been appeared, it is C1, C2, C3, C4 but when I call C1 again (%13), program shows me that C1,... is not assigned. How can I reapair that ?
1
vote
1answer
35 views
Getting a stored variable from its value
Given a numerical value, is it possible to check whether that value is stored in (or defines) some variable in the notebook?
Maybe if I could list all of the defined variables, then I could simply ...
0
votes
1answer
81 views
How to get a function from a numerical integration?
I wold like to know how to get a function from a numerical integration. Here is an example:
h[y_?NumericQ] := NIntegrate[y*Sin[Sin[x]], {x, 1, 2}]
h[2]
Then my ...
0
votes
1answer
39 views
Plot any parametrization (pure function, numbered variables)
I'd like to write a function plot[reg_,f_] that takes as input any product of intervals (list of pairs of reals) reg$\subseteq\!\...
2
votes
1answer
42 views
Assign variable array as function input and generate slider inputs for Manipulate
New to Mathematica. I want to be able to input some parameters, do some calculations, and end up with some output in a functional form such as:
...
1
vote
0answers
309 views
Defining a variable to be greater than zero [closed]
I am trying to do some integrals over a region , however this region is going to depend on parameters $ \alpha , \beta $ and when calculating these integrals they give multiple values depending if $\...
1
vote
1answer
64 views
Table of Variables within Manipulate
Given a certain number n, I want to define n controls within Manipulate with the correct ...
2
votes
1answer
64 views
separation of variables in case of vector components
I have a function f in two variables y and theta, where y=z^2+x^2. There are numerical values for x,z,and theta ( x and z are the dimensions),I have to do calculations to obtain the velocity, so I ...
2
votes
1answer
82 views
Store boolean expression into a variable
My purpose is to use a boolean expression as a requirement that a pattern must comply. The requirement is c1 == "a", and I am using it to select a string from a ...
5
votes
4answers
285 views
Name a list with Table
I am struggling to find a way to assign a value from a list to names from another pre-defined list with Table[].
names = {first, second, third}
...
0
votes
2answers
94 views
Use Alphabet[] as a variable in a function
I'm trying to figure out if I can use the letters contained in Alphabet[] as variables for a function. As a simplified example, I'd like to do something like:
...
0
votes
0answers
50 views
Variables for multiple data files plotting using same Mathematica notebook
I am not an expert in mathematica,
I have this following code. As you see I import a text file under the name "MyPoint1", plot with "pAll" then I do some more calculation with more variables and ...
0
votes
1answer
31 views
Reading and re-assigning variable
I am trying to create a table by iteratively calculating its values using a temporary variable accu:
...
0
votes
0answers
47 views
ReplaceAll Not Working Correctly
I'm trying to use replaceall to redefine my expression in terms of a separate variable..
...
0
votes
0answers
38 views
How to restrict the use of variables to the notebook? [duplicate]
I am solving two problems simultaneously in which the variable x is defined. To the left of the image, i'm solving shape functions and matrix operations. But to the right i'm solving Green's function. ...
1
vote
3answers
69 views
Redefine function after change of coordinates (variables)
I wish to define functions of (possibly) several variables and then apply variable transformations in order to obtain a more comfortable expression. But I run into trouble because I need to redefine ...
0
votes
1answer
59 views
Extract variables from sum of unevaluted functions
I have sums of the form
sum = a f[1,1,0] + b f[1,2,0] + c f[1,2,1] + ...
It is always linear in f[a,b,c]. I would like a ...
0
votes
1answer
46 views
Reversing the flow of the equation sign. Compacting an equation. Choosing which variables to show
Here's a simple example of what I'm trying to get at with that mysterious title.
I start off with a Hermitian matrix that I derived analytically
...
0
votes
1answer
40 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
...
3
votes
2answers
90 views
5
votes
1answer
78 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 $2^n \times 2^n$....
0
votes
1answer
47 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:
...
