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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questions with no upvoted or accepted answers
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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 ...
- 1,607
3
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0
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123
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Variable assignment/replacement issues
I have three questions about variable assignment.
Module[{z},
z = y;
p'[y] /. p -> Function[y, Evaluate[z]]]
When I run the above code, it outputs 0.
1) If I ...
- 569
2
votes
0
answers
72
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how to understand the locality of variables in Mathematica
(in the first i should say may be the title is not very accurate)
how to understand case like the following:
...
- 353
2
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0
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69
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a basic question about variable in Mathematica
I can't describe exactly the problem I'm experiencing, but this kind of problem has a remarkable feature, that is, commands which couldn't work in the before can be executed correctly when i turn off ...
- 353
2
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0
answers
191
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Creating new variable names, Symbol or ToExpression
One can create new variable names by Symbol :
In[1] Table[Symbol["x"<>ToString[i]], {i,1,5}]
Out[1] {x1,x2,x3,x4,x5}
But it is also possible to ...
- 4,285
2
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0
answers
101
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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 ...
- 501
2
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0
answers
834
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How to declare variables with plus/minus sign as subscript/superscript?
I am pretty new to mathematica, so please forgive me if I ask any stupid questions.
I want to create a vector $a^{+}=[a^+_{k-2},a^+_{k-1},a^+_{k},a^+_{k+1},a^+_{k+2}]$ and then do some symbolic ...
- 987
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36
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How to best query if an expression contains Symbol/variable
Say I have this expression, among many:
...
- 181
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92
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Full Information Maximum Likelihood - Under some other name in Mathematica
I have recently stumbled upon something called FIML - Full Information Maximum Likelihood. Apparently this methodology helps overcome missing variables provided the gaps are random. Searching the ...
- 920
1
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answers
55
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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 ...
- 115
1
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101
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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 :
...
- 4,285
1
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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
- 39
1
vote
0
answers
67
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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 ...
- 2,457
1
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43
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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 ...
- 1,265
1
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0
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91
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Execute a notebook with a changing variable
I have created a notebook with one fix variable that I want to run from 1 to 100. Every time the whole notebook (all cells) shall be executed for the given number. At the end of the notebook, it shall ...
- 11
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53
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How to avoid import evaluation until if wil return true
My goal is to import a data from url that depends of 1 parameter, this initialy value is null or undifined en yo have to selec some popup and then the variable has value, what is the method to do that?...
- 89
1
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94
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Settings to disable global scope
I am building a fairly large application in Mathematica, and globally scoped variables are causing issues.
I would like globally scoped variables to be out-of-scope for my expressions, except by ...
- 11
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0
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25
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How to find the argument dependance of an expression
Consider expressions such as
X := f[n[1]][n[3]] g[n[7], n[1923]]
I would like to construct a function that returns the list of $n$'s on which $X$ depends. I know ...
- 375
0
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0
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48
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Identify a condition among variables that satisfy an inequality
I have a symbolic function that produces the output
a = (1 - e - mu/n) Log[(1 - e - mu/n)/(1 - mu/n)] + (e + mu/n) Log[((e + mu/n) n)/mu]
If I substitute ...
- 424
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53
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how to use subscripted variable such as a_i as the control of Manipulate?
I'd like to define a series of variables called $l_1$,$l_2$, etc., in Mathematica, using the "ctrl+_" shortcut. Moreover, I want to use these variables as the controls of a Manipulate[] ...
- 725
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40
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Invalid Variable Error for Solve When Using Law of Cosines
I'm making a shadow simulator, and am using the Law of Cosines to calculate a certain angle in a triangle with two known widths and one known angle. I'm using Solve ...
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66
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Answer changes slightly when re-run
I am trying to resolve why I get slightly different answers when I re-run my notebook. Here is my full code:
...
- 1
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0
answers
51
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Reusing local variables through Reduce and ToRules
Problem: I am interested in solving a system of linear equations through Mathematica. In my current test scenario, I am having trouble using the Reduce function followed by the ToRules command. I ...
- 111
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41
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Scaling a variable multiplied by power series is not giving expected output
I have a power series getting multiplied by a variable, which gets scaled by the small parameter used in the power series. As an example, in the following dummy series:
...
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82
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Cannot Optimize where NSolve and NDSolveValue are involved with Multi-Variables
My Objective Function is Sqrt[Sum[((sol[[j]])^2), {j, 1, noofnode}]/noofnode] with variables v1, v2, v3, v4, v5, v6. But just ...
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139
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How to Optimize a Finite Element Model with Multiple Variables in Mathematica?
Urgent Help, Please !!!
I am attaching my codes for a Finite Element Model which needs to be optimized and the Objective Function ("of" in the code) has been mentioned at the last line of ...
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0
answers
566
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Help with Error: Recursion depth of 1024 exceeded during evaluation
I am quite new to Mathematica. Please excuse my mistakes. I would appreciate if you could help me with the following set of commands.
...
- 1
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answers
43
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how to delete a variable programmatically in a notebook from another notebook
how to delete a variable programmatically in a notebook from another notebook?
c = b;
I have already tried Remove[c] but ...
0
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0
answers
105
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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 ...
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0
answers
54
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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. ...
- 29
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56
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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
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83
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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
0
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0
answers
626
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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 ...
- 1
0
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0
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58
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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 ...
- 121
0
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0
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90
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ReplaceAll Not Working Correctly
I'm trying to use replaceall to redefine my expression in terms of a separate variable..
...
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0
answers
33
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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
...
0
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0
answers
68
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assigning numerical values to variable
I have a csv data file, has two columns of data. First column denotes time (t) and the corresponding value in the second column is flow rate (f). I would like to assign these values to an array f[t], ...
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473
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0
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answers
101
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The conditions used in Sum or ParallelSum: Calling a function/variable
For some reason, I encounter a problem when doing the Sum and ParallelSum (or doing the Do or ParallelDo, e.g. such as the issue here), I figured that the potential cause of the problem can be ...
- 923
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0
answers
91
views
to reduce the unknowns of a set of equations with several symbolic coefficients, e.g. using the GroebnerBasis
I have a set of $4$ equations with $4$ unknowns $\theta_1$ to $\theta_4$, and would like to eliminate the number of unknowns, to get a smaller set of equations, e.g. $n$ equations with $n$ unknowns, ...
- 725
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0
answers
794
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Extract fit error from parameter table to use as a variable
Is there anyway to extract the fit error and store it in a variable. I have done something similar to use actual fit results as
...
- 2,500
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0
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49
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Similar Variable Names
I have variables $X1,...,X10$ and $X1hat,..., X10hat$ in a system of equations. How can I refer to these variables in a summation? I am looking for something like:
...
- 281
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0
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718
views
Colors of variable mathematica
Suppose that I have an equation which goes like this:
x = 2;
yp = 2;
y_p= 2;
a = x + yp + y_p;
Usually, once the variable is defined it will be of blue color and ...
- 303
0
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0
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76
views
Using sub-scripted variables in functions
Is it possible to use subscripts in Mathematica functions, for example
f[Subscript[x, a] _] := x^2
However this doesn't seem to work, is there a way to allow ...
- 2,500
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105
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Best practice for passing variables to many functions?
I am rewriting an application in Mathematica. The previous version used global variables, which I find distasteful, but to avoid it I am needing to pass several static Datasets and Associations around ...
- 407
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1
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129
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Symbolic representation of Class Conditional Probablity as a variable
What is the best way to a create a symbolic variable to represent Class Conditional Probability in Mathematica e.g.
$p(A|B)$
- 275