Questions tagged [hold]
Questions about functions which maintain an expression in unevaluated form, including the use and behavior of Unevaluated, Hold~ functions, Inactive related functions or Hold~ attributes.
248
questions
4
votes
1answer
42 views
Evaluate calls my function multiple times when the function generates an error
If I execute a line of code with Evaluate I find some unexpected behavior when the code returns an error. Here is a minimal example. Let ...
1
vote
2answers
40 views
InputField with Boxes-held formatting fails inside Dynamic
This is an outgrowth of an earlier question.
I have an extensive user interface that has InputFields that I want to hold their specific structure as input by the user (e.g., keeping scientific ...
5
votes
1answer
78 views
Hold[Expression] (or similar) in InputField that truly holds the input unmodified
I am trying to design a user interface where the specific form that the user enters in InputFields are left unchanged. For example, if the user puts in a number in scientific notation, it would be ...
2
votes
0answers
69 views
Non constant coefficient in heat equation
I have to solve the following heat equation over a cylindrical domain.
In cylindrical coordinates the PDE Equation reads:
...
5
votes
2answers
83 views
Obtaining head and parts without evaluation
I have been trying to write a routine MyHead and MyPart
which would have the following properties.
MyHead[2+3]
evaluates to Plus
...
1
vote
1answer
66 views
2
votes
1answer
31 views
2
votes
3answers
101 views
Preventing evaluation of $e^{2i \pi}$
I want to prevent Mathematica from using the identity $e^{2i \pi} = 1$ because at a later step I will evaluating something like $\left(e^{2i \pi}\right)^\alpha$ for some non integer $\alpha$. I wish ...
0
votes
1answer
37 views
Inactive / Activate : basic question of how it works
I would like to understand how Inactive and Activate function works because I'm disturbed.
If I need to inactivate a function and then re activate it how to do it ?
I tried the following which doesn'...
2
votes
1answer
36 views
How can I properly use Catch[] to prevent my program from quitting?
I am getting an error depicting an Uncaught Throw, with the accompanying code being returned:
Hold[Throw[$Failed, CURLLink`Utilities`Exception]]
I have managed ...
0
votes
1answer
64 views
Evaluating function before its plotting
Suppose I want to plot a function $f(x,y)$ but first need to calculate its symbolic expression. An easy solution is to copy the output of my calculation by hand and then paste into ...
0
votes
0answers
57 views
Replace Integrate with NIntegrate
I have a symbolic integral with a pretty complex expression. I need it in symbolic form because I want to compute its derivative.
...
0
votes
1answer
46 views
Evaluation Control for Equation Input to NDSolve
I am trying to numerically integrate a system of equations using NDSolve and am having issues with symbolic matrix inversion taking a long time. The actual system is much more complicated, but I have ...
1
vote
1answer
54 views
Function returning a pattern with condition - how to prevent condition to evaluate prematurely?
I figured it would be convenient to have a function
that returns a pattern, that match equally nested brackets, of the specified type. Such a pattern is easy to create, but I get some error messages, ...
0
votes
2answers
116 views
Mathematica puts function with certain constants on hold, why? [closed]
Here, I probably have a trivial case on how to use functions in Mathematica but I can't figure it out with the help of the Mathematica pages. I define the following function:
...
8
votes
2answers
185 views
How to explain the behaviour of TreeForm?
Just try this:
g=1;a=1;TreeForm[Hold[g[a]]]
The weird thing in the outcome is that the node of g displays 1 ,and a is still a.
I do not know how to explain ...
4
votes
1answer
95 views
Sign of conservative convection coefficient in a formal (Inactive) PDE
Consider the PDE
$$\nabla \cdot (
- \color{blue}{\texttt{c}} \;\nabla u
- \color{blue}{\texttt{alpha}} \; u) = 0
\tag{std}\label{std}
$$
where
...
0
votes
2answers
52 views
How to show the answer in terms of another variable
if we have
A = 1;
B = 44 + 1
output :: B = 45
how we can show B like this
output :: B = 44 + A
2
votes
2answers
82 views
Extract unevaluated definition of function
Say I have a function f[x_]:=a x + b.
Now I want to get the a x + b part from the function to use in e.g. ...
0
votes
1answer
27 views
1
vote
0answers
41 views
Differentiating functions of Set expressions
There are so many things in Mathematica I think I will never understand. Perhaps today there will be one fewer...
B'[y]/.B->Function[y,y^2]
Outputs ...
2
votes
2answers
70 views
How do you change from Traditional form to Input form?
I have something like this:
Hold[TraditionalForm[1/2 + x^2]]
And wish to change it to Input form with the use of code (that is, without clicking Cell > Convert ...
2
votes
1answer
45 views
Strange behaviour (or issue?) in using evaluation of held argument inside a table in Mathematica
I encountered a very strange behaviour on Mathematica using Evaluate on a held argument. Could anyone explain to me what is the subtlety (or is it a bug?)
Here is the expression:
...
10
votes
3answers
179 views
Perform localized, evaluation-leak free replacements
Consider the following expression:
expr = Hold[
{
f[
{1, {Print@1}}
],
g[
{{{Print@1}}}
]
}
];
I'm looking for a way to ...
1
vote
0answers
38 views
How to use Evaluate inside function definitions? [duplicate]
How to use Evaluate inside function definition so that is acts as Evaluate only whet function is called?
This is toy exampl, where I want to define function inside another function:
...
6
votes
5answers
399 views
What is the the proper way to define a function from an expression?
Say after some long computation we get an expression
expr=x^2
We do not know what the value of expr beforehand.
Now we want ...
3
votes
2answers
119 views
Display elementary math without evaluating
Given a list of operators and integers, for instance
oper = {Subtract, Times, Plus}
{a, b, c, d} = {3, 5, 4, 9}
I would like to print
...
1
vote
1answer
73 views
How to stop evaluation of Zeta with even arguments
It could be a duplicate question. However I could not find much after a huge searching.
I have a huge expression in mathematica involving many Zetas.
I want not to evaluate the even Zetas which ...
9
votes
3answers
252 views
HoldForm: Display exactly as entered?
Sometimes, Mathematica's internal representation of expressions can give somewhat surprising results. Specifically, I noticed this when I tried to preserve products of fractions for display.
E.g. ...
0
votes
2answers
54 views
Evaluation control - Hold (?) argument name not argument values
I wanted to produce a list of statistics labelled with the statistic name, for exchange with a database.
I defined
...
2
votes
3answers
91 views
Globally Defining a Variable that Depends on Arguments of Functions [duplicate]
I have many delayed-defined functions of many variables, and all the functions share a term containing some of these variables. Thus, I would like to just call the term ...
3
votes
1answer
52 views
Apply on Message resolves MessageName before applying
I want to make a Message from a List.
Message[LibraryFunction::argx, 1, 3]
...
2
votes
1answer
128 views
Unwanted Hold from recursive function
I am literally copying an example from a tutorial in Mathematica documentation of a recursive function, but when I evaluate I get a Hold. I don't understand why I ...
4
votes
3answers
42 views
Controlling HoldForm while mapping
If I execute
A = {Sin, Cos, Tan}
B = {ArcSin, ArcCos, ArcTan}
#[[1]]@#[[2]]@x & /@ Transpose[{A, B}]
the output is
...
3
votes
1answer
42 views
1
vote
1answer
52 views
RegionPlot: building a list of inequalities
I have a function like this:
Myfunction[x_,y_]:={Max[1, Min[x, 2]], Max[1, Min[y, 2]]}
and I need to do a RegionPlot like ...
3
votes
2answers
86 views
Expanding powers in an expression and Hold
Let an expression like -(1/2) + (3 x^5)/2
be given.
How can this be turned into -(1/2) + (3 x x x x x)/2?
All powers of ...
4
votes
1answer
69 views
How to extract part of a held expression without evaluating it
How can I extract part of a held expression without evaluating it?
Clear[w]
Part[HoldForm[w = 3],1,1]
(* w *)
w = 4
Part[HoldForm[w = 3],1,1]
(* 4 *)
Here I ...
1
vote
1answer
87 views
Replacing one of the integrals in the multiple integral with an analytical solution
Problem consist in simplifying complicated multiple numerical integral, where I know analytical solution for a subset of them. Integrand is of the form
...
4
votes
2answers
143 views
How to customize traditional form for inactive functions?
Let's say I define
Lg[n_]:=Log[2,n].
How do I make
Inactive[Lg][x]//TraditionalForm
output
...
0
votes
0answers
42 views
Editing the function argument
I'd like to construct a function, that changes its own input. The code
...
2
votes
2answers
62 views
Correct way to see domain of function using DownValues?
Here's a simple function g defined for the natural numbers 1 through 10:
Table[g[i] = i^2, {i, 1, 10}]
I now want to find the ...
4
votes
1answer
127 views
How do I make LinearModelFit flexible to number of parameters using FromLetterNumber?
I want to run LinearModelFit where the number of parameters is not fixed. For example, the following
...
0
votes
1answer
58 views
How to delay a function definition in NestList [closed]
I have a code like this. The algorithm is that the original number, 2, has some chance to either be constant 3 or to be 10 times ...
1
vote
1answer
74 views
Evaluate arguments in a curried function left to right
I have an inner pattern
f[g, n_] := inner
and I want to define an outer curried pattern
f[h, m_][f[g, n_]] := ...
which ...
3
votes
3answers
226 views
0
votes
0answers
53 views
2
votes
1answer
44 views
Hold Evaluation in a MenuView or TabView
Suppose I wish to create a MenuView where the evaluation of the rules is time consuming.
How would I delay evaluation of the right-hand-side of the arguments to <...
3
votes
1answer
90 views
HoldForm/Inactivate and exchange operators
I would like to know, how to change parts of a formula in HoldForm.
I have the formula
$$
\underbrace{\prod_{i=1}^N}_{\text{level 4}} \sum_{\sigma_i\in \{-1,1\}}\...
0
votes
0answers
55 views
Trouble with UpSet(Delayed) and IgnoringInactive
I'm having problems setting an upvalue for a symbol that is supposed to ignore Inactive:
IgnoringInactive[f[g[x]]] ^:= match;
...
