Questions about functions which maintain an expression in unevaluated form, including the use and behavior of Hold, HoldForm, HoldComplete, and HoldPattern. Also questions concerning the attributes HoldFirst, HoldRest, HoldAll, etc.

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0answers
70 views

How to “INJECT” with holding Evaluation, specifically into a WhenEvent

I am importing a set of differential and stochastic equations from an external package, and want to use Mathematica to analyse this. I am struggling building the set of equations that I can use with ...
0
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0answers
19 views

Evaluating UnitConvert inside LogPlot

I imported several Physical Quantities with their units and doing single calculations with them works fine and return the right unit, which I can change by UnitConvert[]... For the LogPlot I made a ...
2
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2answers
40 views

Better alternative to Hold/ReleaseHold for postfix application of Monitor

Trying to Monitor a process using the postfix notation, as in Table[Pause[n/10], {n, 5}] // Monitor[#, n] & fails: the ...
7
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1answer
80 views

Matching HoldPattern expressions

My original problem is to delete all rules starts with a[1] from SubValues[a] For example, ...
1
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1answer
64 views

Help on order of evaluation within plot function

it is my first time asking a question here so please let me know if there's anything I should be doing that I'm unaware of. I'm sure the answer to my question already exists on the site but I'm having ...
1
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0answers
35 views

Pretty equations in HoldForm[]

I have been generating equations programmatically, resulting in lists that look like this: {Log[2,(4^4)^3, 3 (Mod[2,4] 4), Log[root[2, 3], 4^4]} where ...
4
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2answers
76 views

MatchQ failing in some cases with Hold [duplicate]

Could someone clarify why the first of these MatchQ finds a match whereas the second does not? (I'm using version 10.0, in case that matters.) ...
3
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3answers
63 views

Replace variable with value prior to evaluating NIntegrate

The title says it all. Reading posts such as this however, I'm not seeing how to do this. This is the simplest example that can show my problem. ...
8
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3answers
175 views

Expand series unevaluated

I'm newbie in Mathematica. I'd like to obtain nice and verbose output for any series calculation. For example, given a simple sequence n*(-1)^(n-1) and ...
2
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1answer
54 views

Evaluate within Hold

When I do... p=3; HoldForm[Evaluate[p]-2] I get: Evaluate[p]-2 BUT I'd like to get: ...
9
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0answers
64 views

Is there a way to TagSet a HoldAllComplete function?

Let's say I want to overload the built-in function Lookup, to handle my data wrapped in myObject. One would use ...
1
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1answer
35 views

Customized `ParallelTable` - Automate `ParallelSubmit` - Possibly an issue with `HoldAllComplete` attribute

Related to this question and in particular its answer I am trying to wrap everything into a new parallelTab function that takes into account some cost per job, ...
2
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1answer
46 views

Recognition Power Head for numeric value

We know: Map[Head, {a, a^2, a^3}] (* {Symbol, Power, Power} *) and Map[Head, {2, 2^2, 2^3}] all of them will be known as ...
8
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4answers
276 views

How to inject unevaluated list of Unique into a RuleDelayed?

I am writing a function that constructs a rule which has Unique[] in the RHS. Here is a simplified segment of code ...
1
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1answer
37 views

ReleaseHold NIntegrate after Replace variable

I would like to calculate the sum of square of two integral(Ex and Ey). I first hold this two integral because two variables(tx, ty) are not specified.Then, I replace tx,ty and releasehold ...
12
votes
1answer
198 views

How to see a code preview (in Experimental`Explore[] or related GUI)

I have been messing around with built in Experimental`Explore[] function. You can call the function in Mathematica yourself to see what it looks like. It is a GUI ...
5
votes
5answers
268 views

Calculating N-th step of recurrent sequence

I am figuring out how to calculate $N$-th step of a square root approximation sequence: $$x_{n+1} = \frac12\left(x_{n} + \frac{a}{x_n}\right),$$ where $a$ is a number the root of which is to be found ...
18
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1answer
217 views

Defer, Hold, Unevaluated, Inactivate — which one when?

What are some guidelines on which function to select from among the superficially similar functions Defer, Hold, ...
3
votes
1answer
60 views

Prevent expression from evaluation in function when using `ToString `

I defined function fhold Clear[fhold] SetAttributes[fhold, HoldAll] fhold[para_List] := ToString[para]; What I want is that ...
2
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1answer
116 views

How to properly define this function of function

I encountered real problem at first, and here is the toy example variable argument stored some expression that is generated from other parts of the program. I ...
9
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1answer
149 views

Why there is only `HoldFirst` but no `HoldSecond`, `HoldThird`, …`HoldN`?

I feel that this must be a duplicate. But I just can't find such a post. Mathematica has HoldFirst, HoldRest, ...
0
votes
1answer
96 views

Replace variable with # and pass function body as an argument to a function

I have a very simple problem, which I would like to make a bit general, but none of my naive approaches have worked yet. This is what I want to do step by step: Define a parameter: ...
4
votes
1answer
63 views

HoldForm -> InputForm without processing the contents

I have programmatically generated a large number of simple equations like 1+1/2. I need them to be 'unprocessed', so they've been run through ...
0
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2answers
120 views

Why does Mathematica Hold my DSolve?

In one cell, I have ...
19
votes
2answers
305 views

Pattern does not match with Orderless head

Why does the following pattern matching not succeed? ...
6
votes
2answers
94 views

Pattern matching an expression involving Times

I'm trying to write a Mathematica function that will format expressions according to my preferences, for example displaying (5 c x)/Sqrt[2] as ...
3
votes
1answer
60 views

How to evaluate an expression via `LinkWrite` when the expression is only known at runtime?

*** Here's the original post... I'm setting up a secondary kernel in sandbox mode with LinkLaunch, and need to pass various expressions to it for evaluation. These ...
3
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1answer
74 views

Table generation with SetDelayed function [closed]

I would like to understand why the following two outputs differ: Let us define the following data set: ...
1
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1answer
55 views

How to achieve fun[Unevaluated[f][Unevaluated[x], Unevaluated[y]] in a more elegant way?

I have defined a function fun[f_[x_,y_]]. When I call it, I want to wrap everything by Unevaluated: ...
2
votes
1answer
61 views

Manipulating unevaluated expressions in nested function calls

This is a follow-up to my earlier question: Passing an unevaluated part of an association to a function I'm trying to create a modular dashboard that controls sound volume of an audio system ...
1
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0answers
21 views

Use functions to call a named object [duplicate]

Now I have several interpolation functions called x30, x50, z30, z50...... I wish to write a function to call these function by inputing x or z and numbers automatically, and assign a argument x to ...
9
votes
2answers
156 views

Passing an unevaluated part of an association to a function

I'm making a UI widget that controls sound volume on a speaker using a slider, e.g.: ...
6
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1answer
74 views

How to force evaluation of an expression with Part left unnevaluated?

My goal is to minimize a real valued multi-variable function averageFreeEnergyDensity. The function accepts an integer argument ...
21
votes
3answers
427 views

Can't inject EncryptedObject

Bug present from 10.0 to 10.3.1 and fixed in 10.4.0 !! Here are minimal examples: ...
4
votes
2answers
216 views
0
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1answer
50 views

Alter evaluation order when applying scalar multiplication to function

Consider the following program: g = 2f; g[x] (* (2f)[x] *) Is there any way I can change the above expression to have it return ...
9
votes
1answer
113 views

FullSimplify Produces Result that Includes Hold

Bug fixed in 10.2.0 In the course of developing a solution to Question 79183, I solved the equation ...
2
votes
1answer
179 views

Nested If statement with unevaluated arguments

I have a list of boolean functions {f1, f2, f3, ...} that take a value and return True or ...
1
vote
1answer
105 views

Printing names of indexed variables instead of values

I'd like to display only the variable (indexed variable) name (in symbol form, not in string form) instead of its value in Mathematica. Say I have a variable foo[i] ...
1
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1answer
67 views

How to prevent automatic simplification in InputField?

Here is a basic example: {InputField[Dynamic[x]], Dynamic[x]} This code generates an input box with and dynamic display. What is disturbing me is that when ...
12
votes
7answers
624 views

How to properly inject iterators into table? [duplicate]

Goofing off on a prior question, I was fiddling with other methods, which led me to the need to inject a constructed set of iterators into a table construct. Now, ...
1
vote
1answer
184 views

How to evaluate some parts of an expression inside Hold? [duplicate]

I want to return a Hold expression but with some parts pre-evaluated. The easiest way to explain this is probably through code example. Here is what I have ...
4
votes
3answers
154 views

Getting terms and only evaluate specific parts

I want to expand the expression but I do not want it to evaluate. Sum[(HoldForm[1/(2 # - 1) - 1/(2 # + 1)] &)[i], {i, 1, 6}] However if you evaluate this you ...
1
vote
0answers
80 views

How to substitute inside Hold? How to create table of summation (with Sigma symbol) expressions? [duplicate]

I would like to create table of summation expressions, which are not evaluated, but summation limits are substituted. I can't accomplish this so far. If I write I get summation expanded. If I ...
5
votes
4answers
301 views

HoldForm does not Hold Form for fractions sometimes

I'm facing a strange behavior of HoldForm. I need to display 1/2*3/4 in LaTeX like this : $$ \frac{1}{2} \times \frac{3}{4} $$ ...
1
vote
2answers
87 views

How to Hold/Defer only one (only given) level?

Is it possible to Hold/Defer some of outer expressions, having evaluates inner ones? For example, I want to prepare a table of expression values, like this ...
0
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0answers
42 views

How to do replacements in Compile'd code? [duplicate]

I want to do something in the spirit of this code: ...
10
votes
2answers
269 views

Held keys in associations

Jacob Akkerboom commented: Note that PositionIndex does work correctly with held expressions, whereas this is a bit painful to implement using ...
5
votes
4answers
325 views

Concatenating strings, unevaluated expressions and evaluated expressions/values

Maybe this is something very simple to some of you. Anyway, I think this can be useful to many others like me. I would like to build an output that involves strings, unevaluated expressions and ...