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.
281
questions
3
votes
1answer
67 views
Performing matrix tensor product and getting a sum of its negative entries
I am given a $3 \times 3$ matrix $M$, which only has real entries.
Is there an efficient way to do the following two operations with $M$?
For a given input $n$, compute the $n$-fold tensor product $M^...
1
vote
1answer
47 views
Define variables dynamically to compute a function
Let's say I have defined a function $W(p, q)$, where $p$ and $q$ are integers between (and including) $0$ and $2$ and the function takes me to a real number.
Upon an input $n$, where $n$ is a positive ...
5
votes
1answer
108 views
Incorrect syntax highlighting? "Variables made special by use in arguments" not working
This example is obviously not useful on its own, but it will cover everything I actually need to know for a more complicated function I'm making.
The example is to recreate the ...
0
votes
1answer
37 views
In DynamicModule, InputField does not display the update when its variable updates through PopupWindow. How to fix this?
Here's a minimal example:
...
2
votes
0answers
21 views
[NDSolve error]: Equation or list of equations expected instead of 0.0001` in the first argument {(s^\[Prime])[t]==-0.325 s[t]-1.5 i[t] s[t]-1.5 [closed]
I am trying to have 5 PDEs with 5 unknowns, with code below
However, I always receive the error message that
Equation or list of equations expected instead of 0.0001` in the first argument {(s^[Prime])...
1
vote
0answers
27 views
Error using list of discrete variables with WhenEvent
I came across an error when using a list of Discrete Variables with NDSolve and WhenEvent. As you can see in the minimal example, where I defined the 'testevent', when I use ...
0
votes
2answers
77 views
Why does this simple code with Eliminate not give any result?
My goal is to obtain the function $s$ defined in the code below as a function of $\chi_1$, $\chi_2$, $\chi_3$. The code runs but never ends, although the problem does not seem too hard to solve for a ...
0
votes
1answer
57 views
0
votes
1answer
43 views
Mean of Randomvariable
I want to calculate Mean[x+y].
x = NormalDistribution[]
y = NormalDistribution[]
Mean[x + y]
...
1
vote
1answer
62 views
0
votes
1answer
32 views
Solve in parametric equations in term of a set of parameters
I am not sure the title is right but let me explain.
I have the relations
...
3
votes
3answers
217 views
Make matrixes with numbered name
Suppose I have two matrixes
M1 = {{0, 0}, {0, 0}}
M2 = {{0, 0}, {0, 0}}
Now I wanna have $N$ matrixes in this form called M1, M2, M3, M4,...MN
How to code to ...
0
votes
0answers
56 views
A function that maps Held symbol to string
Rougly my question is about constructing a function that maps Hold[var] to "var"
even when var has an assigned value. In details :
...
2
votes
2answers
59 views
How can I store vectors in a matrix
I am triying to generate realizations of a Gaussian random process using the KL expansion. For that, I need to multiply an eigenvector for an eigenvalue and a random variable.
I have tried
...
3
votes
1answer
58 views
Definition of multiple variables from a list
I have a list of the form
{{0, 0, 0, 0, 0, 0, a, b, c, d, e, f}, {0, 0, 0, 0, 0, 1, a, c, b, d, f, e}, {2, 2, 2, 2, 1, 2, b, f, c, a, d, e}, ... }
and I would ...
5
votes
1answer
132 views
How to plot solutions of a system of equations by changing colours when one of the variables increases by step?
I have a system of two 3-variable equations $SysEqs=\{f(x,y,z)=0\;,\;g(x,y,z)=0\}$ where the domain of variables are
$$6 < x < 2 \pi \\
- \frac{15}{100} < y < 0\\
0 < z < \frac 32$$
...
3
votes
0answers
76 views
Module inside With, With inside Module, or Just Module?
In general, if one wants to define local variables and local constants, which of the following is the best programming practice in terms of performance and code "safety"? (Assume ...
0
votes
1answer
52 views
Is it possible to plot a 3-variable function, two variables normally, and the third one to change with color?
I have a function like
$$f(x,y,z)=4 \sinh (2 y) \cosh (z-x)+5 \sin (2 x-y)-6 x+y+3 \cosh (2 z)$$
where
$$0<x<4\;,\qquad-3<y<0\;,\qquad0<z<2$$
I would like to have a plot of this ...
1
vote
0answers
31 views
How to change expression of variable in output
I run the example：
c = a - b;
e^(a - b)
This gives me e^(a-b).
How can I do to let it output e^c
2
votes
1answer
51 views
shadowing problem with options of a package
So here is my problem. I am writing a software with mathematica, that uses an external package as a resource. They are some libraries for numerical integration, the CUBA libraries.
http://www.feynarts....
1
vote
2answers
119 views
How to make a change of variable $y=x^2$ in the differential operator $\frac{d^2}{d y^2}$?
I have this differential operator
$$\frac{d^2}{d y^2}\qquad (1)$$
I want to make a change of variable $y=x^2$ in $(1)$ so that I get this differential operator
$$ \frac{1}{4 x^2} \frac{d^2 }{d x^...
0
votes
1answer
31 views
Writing a function with a variable [closed]
trying to write this function, while b,d are known numbers and hj is the variable
thank you very much
0
votes
3answers
96 views
Elimination of the variables
I am trying to get an equation in terms of variable z by eliminating variables g0 and g1 but
Running below code is taking time forever
...
0
votes
0answers
33 views
Automating the re-writing of an expression
I have a function of two variables $f(x,y)$ that I know I can be expressed in the form of a single variable $z=x/y$. Is there a way to write the function in terms of $z$ easily/in an automised fashion ...
0
votes
3answers
39 views
Removing terms with more than 2 variables
Say I have the variable
x = a + a b + a b c + a b c d + ....
What is the easiest way to remove all terms with more than 2 variables? Up until now, I have used
<...
0
votes
0answers
23 views
Minimizing a function and plot it
I have a long expression, depended on 3 different variables say "a", "b" and "p". Just as an example, a part of this expression is: z = p * Cos[x] * Sin[y]. I'm going to ...
-1
votes
1answer
40 views
How to store ParametricPlot in a variable without plotting the graph?
Write separated commands for the following parametric equations using ParametricPlot and plot all of them in a single graph and show the combined graph only.
0
votes
2answers
61 views
Indexed variable - Function that contains summation
I have the following problem:
I have a function that looks like $f(c_1 , c_2 ) = c_1 + c_2 + c_3$.
The variables are $c_1$ and $c_2$, $c_3$ is a known constant. I would like to define a function
in ...
1
vote
1answer
32 views
How can I use Table in a replacement rule? [closed]
I would like to implement the following replacement rule:
$$tr[a^k]^\ell \longrightarrow t[\underbrace{k,k,...,k}_{\ell\ \text{times}}]\,. \tag{1}$$
My (naive) attempt was to write:
...
4
votes
1answer
135 views
Construct 1 variable function from given 2 variable function
Given a function f[x , y].
The definition of f is not self-describing. (f was defined with objects other than f.)
Then I want to construct a function g[x] such that
f[x,y] and g[x][y] are the same, ...
6
votes
1answer
54 views
Automatically set x=0, after each input/output ? ($AfterEachInputOutput)
Is it possible to do something that I want, after each input/output automatically and silently?
I am looking for a feature like $AfterEachInputOutput in the following code :
Example : to set variable ...
0
votes
0answers
41 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
32 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
59 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
79 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 ...
2
votes
1answer
330 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
137 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
52 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
55 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
84 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
91 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
94 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
59 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
51 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
47 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
82 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
67 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
339 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, (\...