Questions tagged [variable-definitions]
Questions on assigning and unassigning definitions to names that represent them, including issues raised by context and localization. Use tag [assignment] for issues relating to Set versus SetDelayed.
448
questions
0
votes
0answers
41 views
Matching two lists and create variables
I have two lists of the same length. One of the lists has all the variable-names in it and the other one is a list of lists in which each list represents a value.
I now want to automatically create as ...
2
votes
2answers
93 views
Unexpected Behavior in `Sum[a + Subscript[a, 1], {a, 1, 2}]`
The simple command
Sum[a + Subscript[a, 1], {a, 1, 2}]
gives the unexpected result
4 + Subscript[2, 1]
while what I want is $3+...
7
votes
2answers
231 views
Copy a function instead of referencing [duplicate]
Is there an option to let me assign the old function of f to g, without changing g when reassigning f?
This piece of code describes my problem:
...
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 ...
0
votes
1answer
32 views
Plot SinglePredictionBands associated with a FittedModel (e.g. LinearModelFit) that is supplied as a variable
I am puzzled about how to plot the SinglePredictionBands associated with a FittedModel (e.g. ...
1
vote
2answers
48 views
Overwrite a tensor product notation a_\[TensorProduct]b_ := KroneckerProduct[a, b]
I noticed that the definition of KroneckerProduct and
For example
TensorProduct[({
{0, 1},
{1, 0}
}), ({
{0, 1},
{1, 0}
})]
Output: {{{{0,0},{0,0}}...
1
vote
1answer
37 views
user-defined functions and "pattern" being returned [closed]
I define a function as
f[J_] := Exp[J^2/2\[Mu]]
but when I try to taylor expand as
k[J_] = Series[f[J] ,{J,0,2}]
I'm getting ...
0
votes
0answers
70 views
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 ...
0
votes
0answers
49 views
a variable as all values from a list
I have a small Problem with lists and variables.
I want mathematica to calculate a formula I derived for 200 values of w between 0 and 5 in ascending order. (maybe I can define w along the lines of)
<...
1
vote
1answer
62 views
1
vote
3answers
92 views
Access to variables in surrounding context from within Manipulate
Suppose you want to access a variable defined in a "surrounding" context (scoped via Begin and End) from within ...
1
vote
1answer
36 views
Changing expression using a new variable definition
If I have an expression that looks like the following:
$$ \frac{i \sqrt{\frac{\sigma _2}{\sigma _1}} \left(-\sigma _2 q_1(t){}^2+\sigma _1 q_2(t){}^2+\left(\omega _2-\omega _1\right) q_2(t) q_1(t)\...
8
votes
1answer
452 views
very simple but unexpected aspect of Function[ ]
I've always thought
(2#+1)&
and
Function[x,2x+1]
are interchangeable in common sense. But,
...
0
votes
0answers
18 views
Partially activate a derivative
Is there a way to make an inactive derivative do some amount of simplification? For instance, say I have
Inactive[D][{{f,g},{u,v}},x]
I would like ...
0
votes
1answer
49 views
Nested usage of NIntegrate
I'm trying to compute an integral of f(x,y) such that an integration over "y" is performed inside the integral over "x". My trial is below:
<...
4
votes
1answer
24 views
KroneckerProduct with arbitrary number of Pauli matrices
I want define a function of n variables as follows
$$f(x_1, ..., x_n)= KroneckerProduct[\sigma^{x_1}, ..., \sigma^{x_n}]$$
where $\sigma^{x_i}=PauliMatrix[x_i]$. Given a number $n$, I can explicitly ...
3
votes
1answer
58 views
Definition of multiple variables from a list
I have a list of the form
{{0, 0, 0, 0, 0, 0, a, b, c, d, e, f}, {0, 0, 0, 0, 0, 1, a, c, b, d, f, e}, {2, 2, 2, 2, 1, 2, b, f, c, a, d, e}, ... }
and I would ...
3
votes
0answers
76 views
Module inside With, With inside Module, or Just Module?
In general, if one wants to define local variables and local constants, which of the following is the best programming practice in terms of performance and code "safety"? (Assume ...
1
vote
1answer
106 views
Solve using PolyGamma function
I am trying to solve for the value of y.
My code is:
x = 0.165;
f = -Log[y] - PolyGamma[0.5 + 0.2*(x/y)] + PolyGamma[0.5];
Solve[f == 0, y]
Running gave me
...
0
votes
0answers
45 views
How to declare a list of symbols as Real numbers?
I have a list of symbols :
gammaVecs =Table[Symbol[StringJoin["gamma", ToString@j, ToString@i]], {j,7}, {i, 40)}];
Which I want to use later in ...
7
votes
2answers
320 views
Is it possible to define conjugate of a function?
Could you help me, please? I have two complex functions of real variable f[x] and fc[x] such that one is a conjugate of another one. I'd like to take a conjugate of an expression that includes both of ...
0
votes
1answer
75 views
How to implement this recursion relation?
I am trying to implement the following relation in Mathematica for any $k$:
$$\begin{align} t_{n,n_1, \ldots, n_k} &= \frac{1}{2} \sum_{m=0}^{n-2} \left( t_{m,n-m-2,n_1, \ldots, n_k} - \frac{1}{N} ...
3
votes
2answers
129 views
Why does f[set_]:=AppendTo[set,5] not work when applying f to a set?
The following code works
ccc = {};
AppendTo[ccc, 5];
ccc
and gives the output {5}
However, the following code does not work:
<...
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, ...
2
votes
0answers
56 views
Certain plotting functions are setting variables unwantedly
I came across the following problem. Certain plotting functions set variables to values, which I do not want. For example, if I run SliceVectorPlot3D with an ...
0
votes
2answers
31 views
Redefining the output of a function
ftn1 = Sin[s]^2 + 3 t^2 + u^5
3 t^2 + u^5 + sin[s]^2
ftn2[s_, t_, u_] := ftn1
ftn2[2, 1, 2]
3 t^2 + u^5 + Sin[s]^2
Hi ...
2
votes
1answer
68 views
Display assumptions of a variable
If I restrict a variable x to x>0 via $Assumptions=x>0, is there a way I can get ...
0
votes
1answer
68 views
Passing symbols, variables and defining functions within functions
Moderators state: “You will be brief and straight to the point”, and so do I.
All codes test whether a polynomial is even or odd, using different approaches.
This works:
...
3
votes
2answers
127 views
Function incorrectly renaming variables in Rule Pattern
Consider the simple pure Function containing a Rule with the named pattern q.
...
1
vote
0answers
34 views
evaluating some of the same variables inside a function while some of them are declared beforehand
This is a style question I suppose, not sure.
Ok so I have this:
a := RandomInteger[{1, 10}];
f[a_] := a - a
f[a]
...
0
votes
0answers
51 views
Proper way to construct a function that takes too long to plot and integrate
Consider the functions phi[t_] and psi[t_] defined in the code below. These are used as basis functions for interpolation ...
1
vote
2answers
108 views
'Do' loop acting on a global variable
I need a code that will allow me to alter a matrix (a global variable) iteratively using a function update (which depends on ...
1
vote
0answers
33 views
Variables with super/sub scripts
So I know how to create variable names with subscripts/superscripts at the end (using ctrl+_ etc), however, how would I use them in the middle of a variable name?
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 ...
1
vote
1answer
63 views
Define/store individual elements of Table output for back-substitution
At its core, mine is a very simple communication error between me and Mathematica that I haven't been able to crack, so I do apologise if it seems embarassingly inane.
Please consider the following ...
0
votes
1answer
50 views
Getting error messages form Set while trying to implement the bisection method with a For-loop [duplicate]
My objective is to build a function using modules that runs the bisection method. I have a working bisection method but when I try to implement it as a module I keep getting this error and I can't ...
1
vote
1answer
39 views
Multiple functions compact form
I have a sort of silly question...
I need to define two functions in the following way
...
0
votes
2answers
82 views
Save a Derivative
I have defined the derivative of a function
Derivative[1][f][x_] := Sin[x]
How can I save this definition in a file? Derivatives are not included in ...
2
votes
4answers
242 views
How can we make the input of a function multiple lists?
I want to create a function that takes inputs that are multiple lists of ordered quadruples. For example, when we run the code our input line should read something like inputs[{2,3,4,5},{6,7,8,9},...} ...
0
votes
1answer
48 views
Compact notations for multiple variables
Why does this work
Manipulate[ListPlot[{a[1],a[2],a[3]}], {a[1], 0, 1}, {a[2], 0, 1}, {a[3], 0, 1}]
But this doesn't?
...
0
votes
1answer
51 views
Defined function keeps the variable
I'm a beginner at Mathematica, and I have a problem finding the roots of a function for a specific variable (using Jens' findAllRoots function).
Due to the nature of my problem, I need to compute ...
6
votes
3answers
184 views
KeyExistsQ[] but for functions?
Is there a good way to check if, say, f[5] has been defined if f is a function, similar to ...
6
votes
3answers
444 views
Create variables in a for loop
I am very new to mathematica, but it would be much easier for me to use For loops in order to create variables. My train of thought was simple, but apparantly does not work. Let's say I defined these ...
2
votes
1answer
55 views
Number of values stored in a function
Suppose I run this:
f[0] = 1;
f[n_] := f[n] = 2 f[n - 1];
f[1000]
Now there will be 1001 values stored in f, and ...
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
...
3
votes
1answer
28 views
Referencing data in sets of sets
Given a data set how to assign definitions to the subsets. For
instance given the data
data = {{0, 1, 1}, {0, 1, 1}, {1, 1, 0}, {0, 1, 1}, {1, 1, 0}}
if {0, 1, 1} ...
14
votes
4answers
833 views
When is a symbol a Symbol? Is there an easy Mathematica way to test if an object is a symbol sort of like a SymbolQ?
Yes I know there is no built-in native function called SymbolQ (but JavaScript does). However, could one be simulated to work for most cases? I often rely on ...
7
votes
1answer
97 views
Is there something wrong with DistributeDefinitions?
I have the following code, which fails to distribute the DownValues for the symbol f. Could anybody please explain what is wrong.
...
0
votes
1answer
92 views
Subscripts use to make expression readable [duplicate]
I am trying to write a function in mathematica which depends on different parameters. For example
$$f(x_1, x_2, x_3, x_4, x_5)= 2x_1+\sin(x_2)+x_3*x_4-x_5^{-1}$$
(My actual function has 12 such ...
