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.
469
questions
8
votes
1
answer
100
views
0
votes
0
answers
37
views
How can I "map thread" similar notation definitions in one line?
In the past few days I have been dealing with different integral notation definitions made by myself. I have noticed several similar notation definitions with a common pattern, but currently I am only ...
- 383
5
votes
1
answer
190
views
Is K is a function? [duplicate]
Some of the capitalized single letters are functions. Starting a fresh kernel and typing in the 24 capital letters, the following letters turn black since they are special functions,
...
- 1,947
0
votes
1
answer
62
views
How to define prefix that can turn numeric?
I put these prefix in my init.m file. First I Unprotect all these symbols, set values and then
...
- 1,862
0
votes
0
answers
29
views
Global assumption non zero
I would like to define globally an assumption stating that I have a nonzero real vector $v$.
For now, I put :
$Assumptions = Element[v,Vectors[{100},Reals]]
but $v$ ...
- 442
0
votes
0
answers
95
views
See variable as byte
I see variable v is occupying 112 bytes of my RAM.
v = {3, 5, 7}; ByteCount[v]
112
Then how to see the content of the 112 bytes?...
- 2,825
0
votes
1
answer
77
views
How to convert mathematica root expression to readable one? [duplicate]
I am trying to find out at what regions a function is monotonically decreasing. The function is a function of X and has two more variables epsilon and B with the constrains 0 < B, 0 <epsilon< ...
- 5
0
votes
0
answers
36
views
How can I prevent functions and variables from being automatically cleared when I close Mathematica? [duplicate]
The following happens with every notebook I make:
I define functions and variables.
When I quit Mathematica and reopen the notebook, all of those definitions have been cleared. The functions and ...
- 1
2
votes
2
answers
152
views
Why is the parametric plot failing?
I tried running the following code but it doesnt seem to be working, it seems to be stuck on running. I think it's got something to do with the way I am defining functions with a variable integration ...
- 123
7
votes
0
answers
102
views
Defining a SparseArray functions in Mathematica 13
I am defining a sparse array as a function of argument x, i.e.
f[x_] = SparseArray[{1->x}, {3}]
In Mathematica 12 this works perfectly, I can pass arguments and ...
- 71
0
votes
1
answer
58
views
Part of array as a blank variable [duplicate]
I have a little question.
Let me define the function:
f[k_]:=k
So 'k' in the argument of 'f' is a blank variable.
Is there a way to define a part of array as a ...
0
votes
1
answer
76
views
Errors appear after integration of an interpolating function
I have a little question about integration of an interpolating function.
There is an error in assumptions of the integral.
I have a function that was obtained with an interpolation method:
...
0
votes
0
answers
84
views
Plot implicit function with intermediate variable
Cross-posted in Wolfram Community.
Here, I intend to plot a 3D picture of
with two implicit functions
where $x, y, t, \xi, \eta$, are variables. Of course, these variables can be constrained to ...
- 93
1
vote
1
answer
69
views
Numerical integration in one variable, of a multivariable interpolation function
I create the following set of data:
newmatrix = Flatten[Table[{t, v, new[t, v]}, {t, 0, 2 Pi, Pi/4}, {v, 0, 1,
0.01}], 1]
where
...
1
vote
1
answer
74
views
expression evaluation for Compile[] too time consuming
I need to use Compile[] for a very large expression to be integrated. But for Compile[] the expression has to be evaluated, and this takes endless time.
The expression is composed of several functions ...
- 135
2
votes
2
answers
85
views
Problems with TagSet
I am new with TagSet and TagSetDelayed and I'm not understanding properly how they works. I introduced the following definition:
...
- 119
0
votes
1
answer
46
views
Is always possible to define a numerical value using subscript?
In this code I defined some values using subscripts and it is not the first time I did this but strangely the code execution crashes. To follow the code.
...
3
votes
2
answers
142
views
Making a list of variables
Consider the following code, which give a Manipulate object that returns the "total" of a certain variable var 1
...
- 4,228
1
vote
2
answers
68
views
Remembering function definitions across sessions to avoid recalculation [duplicate]
I'm working with some large expressions and fourier transforms, which usually take a long time to compute. When I save my notebook with outputs to all my inputs, I'd like it to remember those ...
1
vote
0
answers
46
views
Defining a function expression [duplicate]
I'm sure this has been answered before, but imagine I have the following function
...
- 4,228
0
votes
0
answers
46
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
2
answers
97
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+...
- 923
7
votes
2
answers
252
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:
...
- 563
3
votes
1
answer
75
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^...
- 165
2
votes
1
answer
82
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 ...
- 165
0
votes
1
answer
60
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. ...
- 3
3
votes
0
answers
56
views
Definition of large expression - makes PC freezed
In[1] A=Range[10^4];?A
Out[1] (* definition of A*)
It works for 10^4. But if I increase the number to 10^6
...
- 2,825
2
votes
2
answers
87
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}}...
- 823
1
vote
1
answer
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 ...
- 111
0
votes
0
answers
100
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 ...
- 2,825
0
votes
0
answers
53
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
1
answer
68
views
1
vote
3
answers
102
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 ...
- 389
1
vote
1
answer
55
views
Changing expression using a new variable definition
If I have an expression that looks like the following:
$$ \frac{i \sqrt{\frac{\sigma _2}{\sigma _1}} \left(-\sigma _2 q_1(t){}^2+\sigma _1 q_2(t){}^2+\left(\omega _2-\omega _1\right) q_2(t) q_1(t)\...
- 187
8
votes
1
answer
474
views
very simple but unexpected aspect of Function[ ]
I've always thought
(2#+1)&
and
Function[x,2x+1]
are interchangeable in common sense. But,
...
- 2,825
0
votes
0
answers
21
views
Partially activate a derivative
Is there a way to make an inactive derivative do some amount of simplification? For instance, say I have
Inactive[D][{{f,g},{u,v}},x]
I would like ...
- 1,478
0
votes
1
answer
55
views
Nested usage of NIntegrate
I'm trying to compute an integral of f(x,y) such that an integration over "y" is performed inside the integral over "x". My trial is below:
<...
- 3
4
votes
1
answer
28
views
KroneckerProduct with arbitrary number of Pauli matrices
I want define a function of n variables as follows
$$f(x_1, ..., x_n)= KroneckerProduct[\sigma^{x_1}, ..., \sigma^{x_n}]$$
where $\sigma^{x_i}=PauliMatrix[x_i]$. Given a number $n$, I can explicitly ...
- 251
3
votes
1
answer
65
views
Definition of multiple variables from a list
I have a list of the form
{{0, 0, 0, 0, 0, 0, a, b, c, d, e, f}, {0, 0, 0, 0, 0, 1, a, c, b, d, f, e}, {2, 2, 2, 2, 1, 2, b, f, c, a, d, e}, ... }
and I would ...
- 327
3
votes
0
answers
79
views
Module inside With, With inside Module, or Just Module?
In general, if one wants to define local variables and local constants, which of the following is the best programming practice in terms of performance and code "safety"? (Assume ...
- 1,577
1
vote
1
answer
130
views
Solve using PolyGamma function
I am trying to solve for the value of y.
My code is:
x = 0.165;
f = -Log[y] - PolyGamma[0.5 + 0.2*(x/y)] + PolyGamma[0.5];
Solve[f == 0, y]
Running gave me
...
- 21
0
votes
0
answers
65
views
How to declare a list of symbols as Real numbers?
I have a list of symbols :
gammaVecs =Table[Symbol[StringJoin["gamma", ToString@j, ToString@i]], {j,7}, {i, 40)}];
Which I want to use later in ...
- 912
7
votes
2
answers
352
views
Is it possible to define conjugate of a function?
Could you help me, please? I have two complex functions of real variable f[x] and fc[x] such that one is a conjugate of another one. I'd like to take a conjugate of an expression that includes both of ...
- 153
0
votes
1
answer
86
views
How to implement this recursion relation?
I am trying to implement the following relation in Mathematica for any $k$:
$$\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} ...
- 641
3
votes
2
answers
133
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:
<...
- 707
4
votes
1
answer
155
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, ...
- 2,825
2
votes
0
answers
58
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 ...
- 43
0
votes
2
answers
58
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 ...
- 77
2
votes
1
answer
79
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 ...
- 141
0
votes
1
answer
69
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:
...
- 93