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.
376
questions
1
vote
1
answer
35
views
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:
...
- 445
3
votes
3
answers
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
...
- 790
3
votes
2
answers
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 ...
- 269
1
vote
1
answer
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:
...
- 185
4
votes
3
answers
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 ...
- 3,703
1
vote
0
answers
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'...
- 438
2
votes
1
answer
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:
...
- 254
5
votes
2
answers
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 ...
- 1,085
5
votes
0
answers
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:
...
- 51
7
votes
2
answers
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 ...
- 392
2
votes
0
answers
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 ...
- 131
0
votes
1
answer
61
views
Using Unevaluated to get a list of symbol names
The official documentation of Unevaluated contains the following example:
...
- 5,097
0
votes
0
answers
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 ...
- 1,447
4
votes
1
answer
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 ...
- 135k
4
votes
1
answer
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 ...
- 343
0
votes
0
answers
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 ...
- 343
2
votes
2
answers
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 ...
- 131
1
vote
2
answers
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 ...
0
votes
1
answer
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 ...
- 1
0
votes
1
answer
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:
...
- 2,344
0
votes
0
answers
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 ...
- 438
4
votes
1
answer
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 &...
- 181
2
votes
1
answer
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 ...
- 53
4
votes
1
answer
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 ...
- 2,183
3
votes
2
answers
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 ...
- 5,121
10
votes
1
answer
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 ...
- 3,916
1
vote
0
answers
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 <...
- 21
2
votes
0
answers
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 ...
- 7,163
4
votes
1
answer
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 ...
- 453
2
votes
1
answer
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 ...
- 478
3
votes
1
answer
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 ...
- 2,344
3
votes
3
answers
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:
...
- 7,044
6
votes
3
answers
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) ...
- 7,044
2
votes
3
answers
103
views
0
votes
1
answer
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
...
- 1,087
4
votes
5
answers
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 ...
- 647
3
votes
3
answers
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 ...
- 153
6
votes
1
answer
203
views
Getting terms and only evaluate specific parts of a series
How to write the first five terms of this series in the following form by MMA code?
$\sum_{n=1}^{\infty} \frac{1 \cdot 3 \cdot \cdots \cdot(2 n-1)}{2 \cdot 4 \cdot \cdots \cdot 2 n}= \frac{1}{2}+\frac{...
- 1,921
2
votes
0
answers
90
views
Why does Plot function have HoldAll attribute?
I had an odd issue where my plot wasn't drawn correctly when I called it via Plot[Join[fs,gs], (*..*)]. However, these two versions worked:
...
- 121
1
vote
0
answers
72
views
Why does equal remain unevaluated in this case? [closed]
This is not really an issue but rather a curiosity. Why does
-1 + 1/2 (-1 - Sqrt[5 - 20/9 (-43 + Sqrt[1885])]) + 1/2 (1 + Sqrt[5 - 20/9 (-43 + Sqrt[1885])]) == -1
...
- 647
0
votes
0
answers
102
views
3
votes
3
answers
118
views
Apply HoldForm on only a part of an expression
This expression:
Det[Array[a, {3, 3}]]
is evaluated as:
$-a(1,3) a(2,2) a(3,1)+a(1,2) a(2,3) a(3,1)+a(1,3) a(2,1) a(3,2)-a(1,1) a(2,3)a(3,2)-a(1,2) a(2,1) a(3,3)+a(...
- 174
0
votes
1
answer
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 ...
- 359
3
votes
1
answer
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 ...
- 930
5
votes
3
answers
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[5]
(*15*)
To display what is happening I'm ...
- 1,685
3
votes
1
answer
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 ...
- 251
0
votes
0
answers
57
views
Create a function from another by substituting arguments
Suppose I have a function f[x, coeff]
...
- 291
3
votes
1
answer
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[1]:= rule = j[n1_?NonPositive,n2_?Positive,n3_?Positive]:>AAA
I would like ...
- 501
1
vote
0
answers
111
views
Can't Export string made with StringForm?
This works. It returns "acb".
StringForm["a``b", "c"]
This doesn't work.
...
- 61
0
votes
1
answer
158
views
Derivative with respect to a variable is leaving unevaluated derivatives of functions
I have the following
...
- 91