# 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.

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### Maintaining form of Manipulate to find the formula area of a projected cuboid

I am experimentally trying to solve this problem about the projected area of a cuboid. I sense patterns when I run the below code, but it is difficult for me to compare them. Here is the code: ...
101 views

### Can't get TagSetDelayed to match LHS when the latter has a Hold attribute set

I'm following this example here; Code Readability and Object-Oriented Code ...
122 views

### Showing both the analytical and numerical versions of a matrix

I have found that the Defer function, among others such as HoldForm or Inactive, seems to be the key to something I want to do, but I have been unable to figure out. If I calculate the value of a ...
1 vote
39 views

### How to delay evaluation of Tuples[list,n] when n is a variable to be optimized through NMinimize?

I am trying to do a linear optimization on a variable i where an intermediate variable v is needed: ...
167 views

### HoldForm not working with Map

I am debugging a ListPlot implementation and I need to see the command. To avoid huge list of numbers, i just need the ListPlot ...
1 vote
34 views

### Hold around SetDelayed with Graphics [duplicate]

Minimum Working Example I've defined my own plot function, which does a lot of stuff to the inputs before passing it into the Graphics function. Because of that, I'...
50 views

### How to modify the argument of a specific function below?

I would like to change the values of a and b in the following function: ...
225 views

### Do not understand evaluation order of ReplaceAll [duplicate]

{x, x^2, Length@x, Subsets[x]} /. x -> {1, 2, 3} (* {{1, 2, 3}, {1, 4, 9}, 0, {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}} *) with error What ...
59 views

### Why does MatchQ[Hold[c + b + a], Hold[x_ + b + a]] return False?

Can anyone explain why the following pattern matches: [In1]:MatchQ[Hold[a + c + b], Hold[x_ + b + a]] [Out1]:True But this one fails: ...
184 views

### Map function with evaluated and unevaluated parameters

Let's consider a function with evaluated and unevaluated arguments inside: list1 = {1,2,3} list2 = {x,y,z} fun[list_]:={list,ToString@Unevaluated@list} When I use ...
32 views

### Replacement rule evaluates before substitution [closed]

I have found similar issues in other questions, but none of the answers I found quite do what I want. I have a list of the form list={{x, a}, {y, b}, {z,c}} and ...
61 views

### Using Unevaluated to get a list of symbol names

The official documentation of Unevaluated contains the following example: ...
32 views

### How do I prevent, or get rid of the <code>Abs^\[Prime]</code> in the output of a partial of a Normalize[vector]? 12.0.0 for Microsoft Windows [duplicate]

12.0.0 for Microsoft Windows How do I prevent, or get rid of the Abs^[Prime] in the output of a partial of a Normalize[vector]? The code below shows the problematic ...
60 views

### another problem with context using package and association when using Inactivate

This problem is similar to this problem using package to verify solution of ode with Association, Naming scope/context handling but when I used the solution/trick given there, I still get a problem. I ...
167 views

### Why is Evaluate[] in Plot[] not necessary in some cases?

after reading some related materials(Why do I have to put Evaluate[] here), in my understanding, BecauseAttributes[Plot] has ...
41 views

### Some confusions about Evaluate[] and HoldAll in Plot[] [duplicate]

i can't understand the outputs of the three commands in the following picture. question1: In my understanding, command one Plot[Table[a*x^2,{a,3}],{x,-3,3}] is ...
63 views

### Pattern matching in Association fails in Set assignment

I want to define a symbolic-valued function using Set to memoize the result. However, I get different results when using an ...
1 vote
107 views

### Symbolic manipulations of predefined variables without numerical substitution

As a novice in Mathematica I would like to expand an expression without substituting its variables so that x = 4; y = 4; Expand[(x^2 + y^2)/x^2] generates the same ...
80 views

### Preventing evaluation of $Exp[\pm i\pi]$ until the end of a calculation

I'd like to prevent Mathematica from evaluating $Exp[\pm i\ \pi]$=-1 until I tell it to, at the very end of a calculation. I have a lengthy expression that involves things like (-x+y)^(n), and I know ...
104 views

### Replacing a term according to a given criterion in an expression with non-commutative multiplication (for any sign and location)

There is the following expression: ...
32 views

### DisableFormatting for a single instance of Grid, but format expressions inside that Grid

I have an expression like: Grid[{{ HoldForm[ ... Grid[...] ... ] },{ ... Grid[...] ... }}] This almost gives what ...
99 views

### Holds, Defers, Unevaluated & Inactive

I can program well enough in the Wolfram Language & ignore the nuisances that can pop up... Except Holds, Defers, Unevaluated & Inactive. I never did learn the subtleties of the functions &...
95 views

### Evaluate a double sum using Mathematica

I am evaluating using Mathematica, the double sum $\sum_{u=0}^\infty \lbrace \sum_{k= u+1}^{u+y}[\dfrac{(1-a)}{4} (3/4)^k + 3a[(\dfrac{1}{2})^{k-1} - (\dfrac{3}{4})^{k-1} ]\rbrace$, where $'a'$ is a ...
129 views

### How to construct the HoldAll version of Information[]?

When building other functions I need the HoldAll version of Information, and the usual method seems not to work. Firstly as a ...
128 views

### Understanding HoldAll?

Suppose I try to run the following code: f[x_] := Cos[x] F[X_] := Normal[Series[f[x], {x, X, 5}]] Plot[Table[F[n], {n, -5, 5, 1}], {x, -Pi, Pi}] Mathematica will ...
222 views

### How to programmatically construct a function or a compiled function?

I'd like to programmatically construct a function from a long expression with many duplicate terms. The objective is to programmatically create a set of compiled functions with expressions that were ...
1 vote
55 views

### Plot functions don't allow postfix function execution?

I'm confused about syntax of using // for postfix function execution. It fails in some situations where I would expect it to work. For example, it works with both <...
44 views

### Automatically iconize all Associations in output cells

I work with expressions containing large associations (<|…|>) as subexpressions, and I want to automatically iconize all such subexpressions in all output ...
121 views

### How can I preserve parentheses enclosing a dot product in a HoldForm[]?

I am having a problem with keeping the parentheses enclosing a dot product in HoldForm[]. I want to keep them in my equations since they indicate important grouping ...
78 views

### Visualizing order of operations

TreeForm[HoldForm[ (9-2^2+10 8)/9]] produces this: Is there a way to use Divide instead of ...
94 views

### Terms of expressions with non-commutative multiplication that meet the given criteria

There is the following expression: expr=a^3**x**Transpose[x]**y+x+y**Transpose[y]**x**a^3+x**Transpose[y] It is necessary to apply the ...
269 views

### Different evaluation control inside of Integrate than outside of it

I want to keep inside of a integral evaluated after some replacement inside it, but at the same time the integral itself unevaluated. I start with: ...
273 views

### HoldForm is not working as I would expect

Why HoldForm do this? HoldForm[a/b \[Integral]f[x] \[DifferentialD]x] Output is this ugly looking formula: \frac{a \int f(x) ...
103 views

### Holding after evaluation

Given this little piece of code: ...
91 views

### How to construct the local variables for Block automatically (somewhere in the code)

I am working on the fancy abstraction for Block function. The idea is to use rules to specify which local variable will be used, even if it already defined in the global context like this ...
265 views

### How to define functions using a list of polynomials?

I feel stupid for not being able to do this and I think it is just a syntax error. Let's say i have the following list: L={x,xy,x^2+y,xyz,x^2} How do I define 5 ...
242 views

### Seemingly identical expressions, only one evaluates! [closed]

I am having difficulty using NMaximize with a user-defined function that involves NSolve. Stack Trace shows trouble at the ...
203 views

172 views

### Variable dimension tables with variable ranges

I need to construct a table that has variable dimension and variable ranges (see for tables with variable dimensions and constant ranges, e.g., this question). Suppose there is a list ...
90 views

### A possible issue in combination of the Infix operator ~ with Sequence [closed]

There are other similar questions on this site about using the Infix operator for more than two arguments, which I have read. But there is one thing that I wasn't able to understand and couldn't ...
281 views

### Apply Plus as a new head to a list but prevent evaluation

I would like to illustrate to users the use of Apply with an example. Plus@@Range (*15*) To display what is happening I'm ...
216 views

### How to substitute a random function into a solution of a differential equation?

I would like to solve a differential equation including a source term. The source term is a random variable and I model this by creating a list of RandomReal and ...
57 views

### Create a function from another by substituting arguments

Suppose I have a function f[x, coeff] ...
43 views

### Removing conditions on patterns from LHS of a rule

Let's consider a rule which takes conditions on the patterns specified on the LHS: In:= rule = j[n1_?NonPositive,n2_?Positive,n3_?Positive]:>AAA I would like ...
1 vote
This works. It returns "acb". StringForm["ab", "c"] This doesn't work. ...