Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.

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1
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3answers
128 views

Multiple Plots inside a Manipulate with different dynamic variables on their x-axes

I have an expression with lots of variables, and I would like to make several plots of the expression, where the axis in each is a different variable. The idea is to put them side by side inside a <...
2
votes
0answers
54 views

Estimating processing time for commands

I am trying to evaluate some equations by using Taylor series of expansion (Series[], ExpandAll[], and Normal[] command), and using n equation and n unknown (Solve). Following is not full command (if ...
1
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1answer
53 views

Notebook Initialization

I am running Mathematica 10.2. I am having trouble automatically initializing a notebook. I realize that there have been several other questions/answers on this topic, but the advice given there doesn'...
10
votes
2answers
268 views

The introduction for Context in Wagner's book is out of date? [duplicate]

In Section 8.1.1 (P230 of the book, P249 of the PDF) of Wagner's book, the following example is shown: x = 5; temp`x = 6; Begin["temp`"]; {x, Global`x} The ...
1
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1answer
65 views

How to force evaluation inside the body of a pure function?

For example, I'm writing a function to scale my list of numbers into a specific range. It goes like ...
21
votes
4answers
460 views

Result about Context is inconsistent with the description of “Power Programming with Mathematica”

x = 5; temp`x = 6; Begin["temp`"] {x, Global`x, temp`x} The result in my Mathematica session is {5,5,6}, but it's ...
-1
votes
1answer
59 views

How to plot a function, that is not properly defined in mathematica? [closed]

After rather long and relatively complicated calcuations, I finally got to a point where all my $x(t)$ functions are ...
6
votes
2answers
117 views

What is the Difference Between Rule (->) and RuleDelayed (:>)?

I am new to Mathematica so this question may seem rudimentary. Sorry for that! :) I want to implement the well-known property of Kronecker's Delta $$\Sigma_{i=1}^{n} a_i \delta_{ij}=a_j,\quad 1 \le ...
12
votes
7answers
628 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, ...
8
votes
3answers
183 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 ...
6
votes
0answers
70 views

Why Unevaluated doesn't work on unheld side of Rule/RuleDelayed?

Unevaluated is a function that I never truly understand, and here's one of the cases confusing me: ...
8
votes
1answer
147 views

Why one needs two Unevaluated to show 1+1 correctly in TreeForm?

The task sounds simple, give the tree plot of 1+1. However, after some trying, I can only make this possible by using two Unevaluated. ...
1
vote
1answer
60 views

Convert an evaluated in place code to original

I like "Evaluate In Place," because it hides code and works well. However, I can't figure out how to return to the original code when I want to modify it. I'm sure there is an easy way, but I can't ...
13
votes
3answers
462 views

Handling Kernel quit

One can use $Epilog to do something when the Kernel is quit or put an end.m file next to the ...
0
votes
0answers
44 views

EvaluationMonitor and variables with indices + subscripts

I have encountered the following problem while using EvaluationMonitor with NMinimize: variables that have both a subscript and an index, e.g. Subscript[x,y][1] do ...
0
votes
3answers
209 views

Avoid creation of OwnValues when inserting transformation rules into Experimental`OptimizeExpression

I have a large list of transformation rules that I want to simplify. I find Experimental`OptimizeExpression works as it gets me the answers. My question is: I ...
9
votes
0answers
67 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 ...
8
votes
1answer
926 views

Creating self destructing notebook

Inspired by this post I've been trying to implement the idea in Wolfram with no success yet. I've come pretty close though and need some help. So I've managed to do this: ...
1
vote
0answers
108 views
22
votes
3answers
433 views

Can't inject EncryptedObject

Bug present from 10.0 to 10.3.1 and fixed in 10.4.0 !! Here are minimal examples: ...
8
votes
1answer
218 views

Trouble with polynomial multiplication

Bug introduced in 10.1.0 and fixed in 10.4.0 ...
0
votes
1answer
42 views

Computing approximations of exponential [closed]

I have the code f[x_] := 13 x e^-x bit = Nest[f, 1, #] & /@ Prepend[1]@Range[4, 16, 4] Which I am using to compute values of $f^{(4)}(1), f^{(8)} (1), \...
3
votes
1answer
96 views

Map works but Thread doesn't

This question may be trivial, but I can't get past it for the life of me. I have $n$ matrices of dimension $p_i \times N_i$, with $i$ indexing the $n$-set. I also have $n$ vectors of the appropriate ...
7
votes
2answers
186 views

How to track Part of Symbol or How to symbolize Parts of Symbol without copying data

Let's create simple function: SetAttributes[h, HoldFirst]; h[data_] := Dynamic[Grid[data], TrackedSymbols :> {data}] test = RandomReal[1, {2, 2}]; h[test] ...
13
votes
2answers
377 views

ScheduledTask with scoped variables. Working with timed evaluation

I guess I have to try harder and focus more but timed evaluation always frustrates me. I will show the issue on simple example of delayed trigger. ...
3
votes
1answer
52 views
5
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2answers
151 views

Evaluate numerically an extremely small number

How to evaluate numerically $e^{-4 \cdotp 10^{35}}$ in the form $0,a_1a_2...\times 10^{-n}$ ...
4
votes
1answer
72 views

Strange behavior of ArcTan [duplicate]

I've noticed a strange behavior of Mathematica's ArcTan function with two arguments. If both arguments are 0 or ...
2
votes
1answer
50 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 <...
1
vote
0answers
43 views

How can I use x->Root outputs from Solve? [duplicate]

Do not understand the meaning of the output given by Mathematica to this equation: ...
0
votes
1answer
51 views

Manipulate curves [duplicate]

I want to draw curves with manipulation. When I use the following code, I receive nothing. ...
6
votes
0answers
49 views

How trap expression that doesn't evaluate?

If evaluating an expression produces an error, it's easy to trap that using Check or Throw......
1
vote
1answer
37 views

Access variable middle of the run [duplicate]

I execute a Table[] that need large time to be finished. If I abort it I loose what evaluated until now. Does it possible to stop running and save what evaluated ...
12
votes
1answer
889 views

Why is this 2D plot so slow?

I first do a 3D Plot of four surfaces (eigenvalues of a $4\times4$ matrix) over $kx,kz$ (setting $ky=0$ all along). And then I try to give a 2D plot along three connected particular lines in $kx,kz$-...
11
votes
4answers
194 views

Evaluation of Alternatives

I recently stumbled upon a few examples that suggest patterns containing Alternatives do not evaluate for individual alternatives. For example: ...
1
vote
0answers
77 views
7
votes
1answer
311 views

How is LHS = RHS; … ; LHS (nontrivially) different from … ; RHS

I'm trying to understand how Mathematica thinks about the results of Set. Suppose we perform LHS = RHS. I'm focusing on when ...
0
votes
0answers
42 views

Substitute arguments before evaluating variables in Block [duplicate]

Suppose I have f = x^2; mod[x_] := Module[{}, f] Then mod[3] returns x^2. Is there any way to tell Mathematica to treat the "x" inside of f as the same "x" as ...
1
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0answers
57 views

Solving a polynomial equation with an approximate constraint is slower than the symbolic solution

Why do these two operations have such different timing, when the only difference is specifying r as approximate $0.1$ vs arbitrary-precision $1/10$? Here are the ...
1
vote
1answer
88 views

How can I draw truth tables using Mathematica [duplicate]

For instance, the given expression p ⊕ (p v q) In the problem I'm trying to solve. There's a Mathematica answer to this: ...
15
votes
3answers
2k views

How to evaluate the $0/0$ type limit in Mathematica?

When I use Limit to evaluate the limit $$\begin{align}\lim_{k \to 0} \frac{ (k+2)(\alpha^2 - \sqrt{\alpha^4 + k}) + k}{\alpha^2 - \sqrt{\alpha^4 + k} + 2 k}\end{...
0
votes
0answers
40 views
10
votes
2answers
284 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 ...
6
votes
1answer
115 views

Why do certain fractional values in TriangleWave not evaluate?

While answering another question I discovered that TriangleWave does not automatically evaluate when given certain fractional values, specifically fractions with a ...
2
votes
1answer
98 views

Clearing a global variable from inside a Module

This is a highly simplified version of a initialization problem I have with a complicated program with many (about 100) modules. If one enters: X=42; Clear[X]; the ...
1
vote
2answers
72 views

Evaluation of a list

I'd like to assign to $a[1],\ldots,a[m]$ ($m$ being defined beforehand) zero values. I tried Table[a[i], {i, m}] := Table[0, {m}]; but got an error message <...
10
votes
4answers
454 views

Order of evaluation - does Mathematica evaluate variables before or after substitution?

Let's say I write y = x^2; x = 10; z = y + y^2 + y^3 Does Mathematica internally evaluate y before or after substituting it into z? I.e., does Mathematica ...
4
votes
2answers
62 views

Controlling evaluation in a custom summation function

I'm doing some computations that involve summations with many indices over the same range - consider the simplified example Sum[a[i,j],{i,1,2},{j,1,2}]. To prettify ...