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.
234
questions
24
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
367 views
When to name a variable with $
There are some symbols in the Wolfram Language that start with $, including $Abort, ...
14
votes
3answers
394 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
500 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
977 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
658 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:
...
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
280 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
469 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 ...
6
votes
3answers
461 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
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
...
6
votes
2answers
264 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
182 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
852 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
1answer
217 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
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]
...
5
votes
4answers
255 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
90 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
1answer
241 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!
5
votes
2answers
449 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
342 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
404 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
691 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
250 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
133 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
177 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
166 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
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
119 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
54 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 $2^n \times 2^n$....
3
votes
1answer
575 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
645 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
86 views
3
votes
2answers
118 views
3
votes
1answer
82 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
481 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
...
3
votes
1answer
143 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
146 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) ?
3
votes
1answer
456 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 ...
3
votes
1answer
13k views
Explanation for coloring of variables by code editor?
I was working on some homework just now, and I realized that some of my variables have different colors, and I am not sure why.
In the example below f is black, ...
3
votes
2answers
155 views
Using a variable for two different purposes
I want to name a bunch of tables after the OEIS entries which describe them.
Is there any way to use these names for both the table name and the link at the same time?
The second line uses the ...
3
votes
2answers
96 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
2answers
228 views
3
votes
2answers
94 views
Treat 2 variable as 1
Is there anyway to treat two variable, that are a result of expansion, as one?
To use Solve[] I can do
...
3
votes
1answer
567 views
Protected Variable Error with Workbench 3.0
I have Wolfram Workbench 3.0, build 78, with Mathematica 10.4 as the front end. I am using Windows 10. I am trying to run a simple test source code test.m:
...
3
votes
0answers
559 views
Multiple variable assignment from a list
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
0answers
55 views
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 ...
