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1
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1answer
48 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 ...
0
votes
0answers
12 views

why does a ReplaceAll stop Plot from cycling colors? [duplicate]

Suppose I Plot[{a x^2, a x^3} /. {a -> 2}, {x, 0, 1}]. Then the expressions plot, but the colors do not cycle. If I Evaluate ...
4
votes
3answers
136 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 ...
4
votes
2answers
200 views

HoldForm[Operator ##] on some list

Recently in response to this question Mr.Wizard suggested an unusual way to summing numbers. This doesn't seem to be documented. ...
1
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0answers
39 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
178 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
53 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 ...
14
votes
4answers
355 views

Prevent graphics render inside held expression

Assuming each odd line is input I would like the even lines to be the output of the following lines. In the above the Graphics are inside ...
25
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3answers
616 views

Changing Values in an Association using Map

I am trying to change the value of one key in an association based on the value of another key in that association. So if my association starts as: ...
0
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0answers
41 views
6
votes
1answer
99 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
228 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 ...
1
vote
2answers
64 views

Pattern matching to head with HoldFirst

I want to define a function that only operates on expressions with a head from a given list, such as f[expr:(_And|_Or)] := Print["LHS is ", expr[[1]]]; This of ...
11
votes
2answers
647 views

Displaying a series obtained by evaluating a Taylor series

Description of problem I would like to use Mathematica to display the series obtained by substituting a value for $x$ in a Taylor series expansion. The terms of the series will be rational numbers, ...
0
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3answers
92 views

Create polynomials from Series

This question actually doesn't have quite a lot to do with the Series function, but I don't know how to describe my problem. So here's the thing. I'm trying to ...
3
votes
2answers
120 views

Converting unevaluated lists to strings

I have a list like l = {2 - 3, 12 - 4, Times, aab} I want to end up with {"2-3", "12-4", "Times", "aab"} I have tried ...
1
vote
1answer
77 views

Retain original form of formatted equation [duplicate]

I am having trouble getting Mathematica to retain my original equation form. For example: As you can see, even though I use HoldForm, it still changes the style of my equation. Very frustrating.
11
votes
4answers
300 views

Replacing parts of a held expression with held parts of another expression

I'm applying the Trott-Strzebonski technique in order to replace inside a held expression. ...
1
vote
1answer
99 views

How to operate with function body without evaluation

I have several functions (let a[x] and b[x]), defined as expressions with integrals and differentiations. I want to perform some ...
7
votes
4answers
159 views

Hold expression with RandomInteger

One more question for today: I'm trying to show two random integers with a plus (+) sign between them, in an unevaluated form. I know how Hold and HoldForm work, but they hold everything, including ...
2
votes
1answer
132 views

Applying rules to rewrite expressions that contain patterns

I'm trying to write a rule that can rewrite a pattern that exists in another expression. For some reason, this is proving to be more challenging than I expected ... most likely because I'm not totally ...
8
votes
1answer
202 views

Why does Plot[Hold[x], {x,0,1}] work?

It appears that, counter to my expectation, all of these (and probably many others) seem to work fine: ...
3
votes
2answers
153 views

Stopping a head from evaluating more than once

While attempting to answer my own question, Is there a way to "hold" prefix / infix / postfix notation?, I came across the need to evaluate a recursive function only one level deep. For ...
3
votes
1answer
119 views

How do I get the length of held list without evaluating the list?

I used Extract with Hold to retrieve a sublist containing expressions I didn't want evaluating, e.g. ...
1
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0answers
67 views

How to extract a variable names (not values) from a list of transformation rules?

I am trying to extract variable names from a list of transformation rules mapping = {var1 -> 'val1', var2 -> 'val2' }. Variables ...
0
votes
1answer
329 views

Pass unevaluated function with evaluated arguments

I am almost sure that this question has been asked somewhere. I found similar ones, but I cannot find exactly what I need, which might mean that I am on the wrong track. I search a method to pass an ...
1
vote
2answers
276 views

Converting expression into string without evaluating it

How can one convert a Mathematica expression into a string without the expression being evaluated first? I tried using Hold, but it returns ...
3
votes
1answer
46 views

Table doesn't replace inside conditionals (If, Which) [duplicate]

This: Table[If[cond, y], {y, 1, 3}] outputs this: {If[cond, y], If[cond, y], If[cond, y]} The ...
7
votes
3answers
168 views

Converting StringJoin to StringForm inside Hold

Let's say I have a piece of code: Hold[{code1, "asdad " <> ToString[testa] <> " adsd " <> ToString[testb], code2}] (*MWE ofc*) ...
3
votes
2answers
75 views

Confused with HoldForm in Postfix notation

Why does the following code produce different result? In my mental model, they should be the same. ...
4
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4answers
510 views
3
votes
1answer
100 views

Why is held expression evaluated?

Context: I'm studying non-linear dynamics. As part of a bigger problem, I'd like to generate lists of the form {{deq, ic1}, {deq, ic2}, ...}, where ...
1
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0answers
64 views
11
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3answers
187 views

Creating a custom context with a Hold construct

I'm trying to create a function "InContext" to execute a piece of code inside a certain context (and to return the result of evaluating that piece of code). One approach is to place the code inside a ...
1
vote
1answer
131 views

Evaluation of second argument to NIntegrate

Apologies if this is a duplicate, but I couldn't find it. The expression Integrate[x^2, Flatten[{{x},{1,2}}]] evaluates properly, to $\frac{7}{3}$. However, ...
6
votes
4answers
290 views

Is there a more Mathematica-y way to label these plots?

I am studying an infinite square well in the context of quantum mechanics. ...
1
vote
1answer
161 views

Passing a joined list of symbols for Module or Block to treat as its own local symbols

The Question I'd like to write a function which itself takes a list of symbols, e.g. Foo[{x, y, z}] to pass to Module ...
3
votes
3answers
86 views

Operations on expressions within Hold [duplicate]

I want to convert {Hold[1 + 2], Hold[3 + 4], Hold[5*6]} into Hold[{1 + 2, 3 + 4, 5*6}]. I have tried ...
2
votes
1answer
222 views

Why is this expression being held, and how can I evaluate it?

I can't figure out why an expression isn't evaluating, even though there's no Hold* in its FullForm: ...
2
votes
2answers
108 views

Extracting variables from Hold expression

For example I have some global assignments x=1;y=2;z=3 and an expression Hold[x*y/z]. How can I now extract variables ...
7
votes
6answers
200 views

How to join held Lists?

Let's say I have a = Hold@{2+2} b = Hold@{4+4} How can I get Hold@{2+2,4+4} ie join the two held lists ? More ...
0
votes
2answers
114 views

Assigning several values inside DynamicModule

I have coded a model that contains several parameters. The parameters can be changed interactively by the user using an interface contained in a DynamicModule[]. There are several "basic states" of ...
40
votes
3answers
984 views

Replace inside Held expression

I wish to make functional replacement inside Held expression like this: ...
5
votes
1answer
81 views

Why is NHoldFirst not propagated to symbolic derivatives?

I encountered a nasty problem that N cannot evaluate expressions containing a symbolic Derivative of a multi-parameter function ...
0
votes
0answers
128 views

How to evaluate only arguments, but leave topmost expression unevaluated? [duplicate]

I want to represent expressions mostly in unevaluated form, but being able to evaluate it's subparts. For example, how to evaluate only arguments, but leave topmost expression unevaluated? For ...
19
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5answers
2k views

How to pass a symbol name to a function with any of the Hold attributes?

Given a function with the attribute HoldFirst, HoldAll or similar, and a variable, list, how ...
5
votes
3answers
223 views

Applying a function with the HoldAll attribute inside NestList

I'm trying to write an update function, which can be applied to a list and then to NestList it. As the function has to manipulate the given variable I figured I ...
1
vote
1answer
147 views

direct assignment to the element in a Table

I have already asked a related question here why set values in this way doesn't work? But I think I have to write the question which I encountered explicitly? ...