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.
253
questions
25
votes
5answers
5k views
Extracting variables from an expression
I'm looking for a way to extract a list of variables from an expression, for example with an input like:
...
17
votes
2answers
415 views
When to name a variable with $
There are some symbols in the Wolfram Language that start with $, including $Abort, ...
16
votes
3answers
441 views
For any symbol, how can I get the full context-qualified name of the symbol as a string?
I'd like to have a function, whether built-in or not, that when given a symbol, whether bound to a value or not, returns a string giving the context and name of the symbol.
Example: ...
13
votes
1answer
12k views
Get expression type?
Is there a built in function that distinguishes between different kinds of variables?
I mean something like:
VariableType[ 123 ]
Number
...
11
votes
2answers
537 views
Is there a convention on which name to use for a throwaway variable? (Like underscore in Python) [duplicate]
I would prefer to write {_, foo} = LongFunctionName[arg1, arg2] instead of foo = LongFunctionName[arg1, arg2][[2]] or ...
10
votes
6answers
1k views
Generate list of strings from a list of assigned variables
How do I generate a list of strings from a list of assigned variables?
E.g. convert
...
9
votes
1answer
2k views
What is and isn't a valid variable specification for Manipulate?
I have an expression whose terms have arguments (representing subscripts), like this:
myExpr = A[0] + V[1,T]
I would like to put it inside a ...
9
votes
1answer
734 views
Why does one of my Manipulate integer variables get turned into a real?
Bug introduced in 9.0 or earlier and persisting through 11.0.1 or later
I'm developing code for manipulating graphs. Spot the difference in the 2 Manipulates below:
...
8
votes
4answers
1k views
Assign values to variable names in lists [duplicate]
I hope somebody can help me in this (I guess) simple question: I have a list of variable names
ls={w0,w1,w2}
and another list of values
...
7
votes
5answers
1k views
Checking if all the variables are present in the defined function
I want to check if a user input the function with all the specified variables or not. For that I choose the replace variables with some values and check for if the result is a number or not via a ...
7
votes
2answers
317 views
Apply ToString to a list of variables [duplicate]
I have
data1 = {1, 1};
data2 = {2, 2};
datalist = {data1, data2};
I want to create a string list based on the variable names inside ...
7
votes
2answers
2k views
Display variable name instead of value
Is there a way to display the variable name instead of its value? for example, I need something likevarname = 1; function[varname]; and the output is ...
7
votes
2answers
519 views
Ignore some values at return
Is there Mathematica analogue of Python _ (underscore) or Matlab ~, a special variable, that can be used when a function returns ...
7
votes
1answer
220 views
Tremendous bug using EstimatedDistribution (using NMinimize) in v8.0 and v10.2
Let's define F4 and estimate the distribution of the data:
...
6
votes
3answers
469 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]
...
6
votes
2answers
269 views
Want to return name of last defined variable without explicitly naming it
Suppose I have this code:
dec = 7.1 + 6.6 + 27.2 + 66.5
jan = 7.1 + 6.6 + 27.2 + 66.5 + 65.7
feb = 7.1 + 6.6 + 27.2 + 66.5 + 65.7 + 69.7
And I want MMA to return:...
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 ...
6
votes
1answer
271 views
An alternative to subscripts?
Are there any good alternatives to using subscripts to keep track of and uniquely identify many variables? I know that subscripted variables behave badly.
Thanks!
6
votes
1answer
905 views
Variable number of nested variable-range sums
I would like to express the following nested sum in Mathematica:
$$
S(m,j,N) =
\sum_{k_1=m+j-1}^{N-1} f(N,k_1)
\sum_{k_2=m+j-2}^{k_1-1} f(k_1,k_2)
\cdots
\sum_{k_m=j}^{k_{m-1}-1} f(k_{m-1},k_m)
$$
...
6
votes
0answers
64 views
Nested rules and automatic renaming of variables [duplicate]
I understand why $ happens here:
ClearAll[foo]
foo[a_] := (x_ :> a x)
foo[1]
...
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}
...
5
votes
1answer
99 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. ...
5
votes
2answers
637 views
Series expansion of a multivariable function to an order n for any number of variables [duplicate]
Suppose I want to expand a multivariable function to an order n.
...
5
votes
3answers
376 views
One inequality with two variables
I would just like to know if this:
((a - b)/(b*Log[b])) - Log[Log[a]] + Log[Log[b]]
exceeds 0 for any combination of a and <...
5
votes
1answer
409 views
How to make Mathematica express an equation in terms of previously defined functions
I was given a problem for my physics class, and perhaps I have taken it too far, but I wish to finish what I started. I have a function (i warn you that this does not look pretty)
...
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 $2^n \times 2^n$....
5
votes
1answer
716 views
How to re-assign values to a List of variables?
The accepted Answer to this similar Question can only be used one time, so it's not suitable for my problem.
I do high-dimensional calculations for which I need to make lists of variables, like so:
<...
4
votes
1answer
253 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 ...
4
votes
1answer
134 views
Map[Remove[#]] doesn't seem to do anything
If you have a symbol with a value, you can clear it with Remove[]. Thus
...
4
votes
1answer
189 views
Context inside Do[…]-loop
Consider the following code:
Begin["mycontext`"];
myvar = 7;
Print[Context[]];
Print[Context[myvar]];
End[];
with the output
mycontext`
mycontext`
Now ...
4
votes
2answers
6k views
Using Array Elements as Function Arguments
Suppose I have an array
p = {a,b,c,d}
and a function f that takes a variable number of arguments. I want to evaluate
...
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]]
...
4
votes
2answers
191 views
How to find variables set through Get[“/some/path/dump.mx”]? [duplicate]
(NB: I could not find any good tags for this post. Please feel free to add better ones.)
Suppose that the file /some/path/dump.mx was generated during an earlier ...
4
votes
2answers
621 views
Combining Multiple Lists
Let's say I have 4 lists:
list1 = {a,b,c,d};
list2 = {e,f,g,h};
list3 = {i,j,k,l};
list4 = {m,n,o,p};
I can combine them using Join
...
4
votes
1answer
480 views
Is it possible to find the size of a variable in a notebook?
I have a fairly large a list of matrices matsLst, which takes about 15 minutes to compute (but computes successfully each time). I can test in the notebook that ...
4
votes
2answers
241 views
4
votes
1answer
147 views
Checking if input is a function
I would like to write a program to find the leading coefficient of a given polynomial. (Sounds easy, right?) I'd like to be able to handle the format x^2-x+7 (with ...
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:
...
4
votes
0answers
635 views
Multiple variable assignment from a list [closed]
For example in Python, if we have a list of 3 elements, say ls = [1,2,3] and we want to assign a variable to each value (from left to right), one can do as follows: ...
3
votes
1answer
728 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).
...
3
votes
3answers
813 views
Getting a list of variable names as strings via a function
This is a new twist of an earlier question about how to get variable names as strings from a function.
I would like to have a function that returns a list of variable names, each being a string, from ...
3
votes
2answers
90 views
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, ...
3
votes
2answers
218 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 ...
3
votes
2answers
118 views
3
votes
1answer
88 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 ...
3
votes
2answers
173 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.
...
3
votes
3answers
438 views
Creating a List of Symbolized Indexed Variables
I am trying to creat a list of indexed variables (symbols) using the Notation package and Symbolize command.
As an example, ...
3
votes
1answer
163 views
How can we define lots of variables
I am new to Mathematica and some things I do not understand. Right now I need to write an algorithm which takes a polynomial in many variables, I denote it by $p_{i,j}$, and then I want to apply a ...
3
votes
1answer
187 views
Transformation of variables in function in mathematica
How do i change variables of function in mathematica ? for example of
f(p,q) = p^3 + q^3, from p,q to x= p-q and y = p+q, so that the function now becomes f(x,y) ?
