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.
459
questions
-1
votes
0answers
59 views
Numeric integration with symbolic boundaries
The following is a definition of a numeric integration:
...
0
votes
1answer
55 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
1answer
54 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
0answers
77 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 ...
1
vote
1answer
54 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
1answer
65 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 ...
2
votes
2answers
83 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:
...
0
votes
1answer
43 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
2answers
136 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
...
1
vote
2answers
67 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
0answers
45 views
Defining a function expression [duplicate]
I'm sure this has been answered before, but imagine I have the following function
...
0
votes
0answers
45 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
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+...
7
votes
2answers
243 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
72 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
62 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
46 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
59 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
74 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
51 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
67 views
1
vote
3answers
94 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
41 views
Changing expression using a new variable definition
If I have an expression that looks like the following:
$$ \frac{i \sqrt{\frac{\sigma _2}{\sigma _1}} \left(-\sigma _2 q_1(t){}^2+\sigma _1 q_2(t){}^2+\left(\omega _2-\omega _1\right) q_2(t) q_1(t)\...
8
votes
1answer
460 views
very simple but unexpected aspect of Function[ ]
I've always thought
(2#+1)&
and
Function[x,2x+1]
are interchangeable in common sense. But,
...
0
votes
0answers
18 views
Partially activate a derivative
Is there a way to make an inactive derivative do some amount of simplification? For instance, say I have
Inactive[D][{{f,g},{u,v}},x]
I would like ...
0
votes
1answer
52 views
Nested usage of NIntegrate
I'm trying to compute an integral of f(x,y) such that an integration over "y" is performed inside the integral over "x". My trial is below:
<...
4
votes
1answer
24 views
KroneckerProduct with arbitrary number of Pauli matrices
I want define a function of n variables as follows
$$f(x_1, ..., x_n)= KroneckerProduct[\sigma^{x_1}, ..., \sigma^{x_n}]$$
where $\sigma^{x_i}=PauliMatrix[x_i]$. Given a number $n$, I can explicitly ...
3
votes
1answer
60 views
Definition of multiple variables from a list
I have a list of the form
{{0, 0, 0, 0, 0, 0, a, b, c, d, e, f}, {0, 0, 0, 0, 0, 1, a, c, b, d, f, e}, {2, 2, 2, 2, 1, 2, b, f, c, a, d, e}, ... }
and I would ...
3
votes
0answers
78 views
Module inside With, With inside Module, or Just Module?
In general, if one wants to define local variables and local constants, which of the following is the best programming practice in terms of performance and code "safety"? (Assume ...
1
vote
1answer
117 views
Solve using PolyGamma function
I am trying to solve for the value of y.
My code is:
x = 0.165;
f = -Log[y] - PolyGamma[0.5 + 0.2*(x/y)] + PolyGamma[0.5];
Solve[f == 0, y]
Running gave me
...
0
votes
0answers
50 views
How to declare a list of symbols as Real numbers?
I have a list of symbols :
gammaVecs =Table[Symbol[StringJoin["gamma", ToString@j, ToString@i]], {j,7}, {i, 40)}];
Which I want to use later in ...
7
votes
2answers
330 views
Is it possible to define conjugate of a function?
Could you help me, please? I have two complex functions of real variable f[x] and fc[x] such that one is a conjugate of another one. I'd like to take a conjugate of an expression that includes both of ...
0
votes
1answer
82 views
How to implement this recursion relation?
I am trying to implement the following relation in Mathematica for any $k$:
$$\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
143 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
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 ...
0
votes
2answers
51 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
71 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
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:
...
3
votes
2answers
138 views
Function incorrectly renaming variables in Rule Pattern
Consider the simple pure Function containing a Rule with the named pattern q.
...
1
vote
0answers
35 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
55 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
119 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
68 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
54 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
88 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 ...
