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

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7
votes
1answer
197 views

How can I have interruptible computations inside a manipulate?

Here's a perfect example of my problem: Manipulate[Pause[n], {n, {1, 10}, ContinuousAction -> False}, SynchronousUpdating -> False] It is illustrated by ...
7
votes
1answer
94 views

Strange behavior when setting NumericQ of a symbol

It happens both in v9&v10. If you try this a^0 a^0 (1/a)^(3/2) a^0 (1/a)^(5/2) Mathematica returns 1 (1/a)^(3/2) (1/a)^(5/2) It's trivial. ...
7
votes
2answers
149 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] ...
6
votes
2answers
623 views

Normal[Series[ ]] does not give a normal expression

Let us say I want to show how the Taylor's series for Sin behaves: ...
6
votes
3answers
1k views

Keep function range as a variable

Plot[2*x^2 - x + 2, {x, -1, 1}] plots a function of x from -1 to 1. As far as I can see, I cannot "save" this range in a variable: ...
6
votes
2answers
171 views

Difference between Evaluation>>Quit Kernel and Quit[]

What is the difference between Evaluation >> QuitKernel and Quit[]? Both seem to quit the kernel (and clearing all ...
6
votes
2answers
303 views

Why is CityData[All, “Coordinates”] failing?

When I evaluate CityData[All, "Coordinates"] Mathematica returns {Missing["NotAvailable"], Missing["NotAvailable"]} ...
6
votes
3answers
119 views

Evaluate a expression split in a list

I have a list with this format {integer, sign, integer, sign, integer}, sign being one of these: Plus, Subtract, Times, Divide. For example, let's say: ...
6
votes
2answers
220 views

Evaluation in lambda function

If I have a function, that returns a function, for example: f[a_] := a^2 * # & then f[3] == 3^2 # & Is there a way ...
6
votes
5answers
877 views

Prevent Part[] from trying to extract parts of symbolic expressions

If you have a list, e.g. {1, 2, 3} then you can extract the $k$th part using Part (...
6
votes
2answers
472 views

How Can Notebook Know When it Called by Another Notebook?

I would like a notebook to behave slightly differently depending on whether it is evaluated from another notebook; i.e., ...
6
votes
2answers
209 views

Why does Mathematica appear to change the head of certain expressions?

I don't know if the question trivial or not (if so I will delete it), but here is what I have: I know that x x (* x^2 *) Looking at the full form gives ...
6
votes
2answers
146 views

Partial result of aborted evaluation of FullSimplify

When FullSimplify invoked on a large expression, it can run for hours. If I do not have time to wait, and abort the evaluation, I get no result, although, ...
6
votes
2answers
530 views

How do I make NotebookEvaluate work inside Button?

The following creates a button to select a notebook to run. When the button is pressed it seems that Mathematica finds the notebook but cannot evaluate it. The following error occurs Could not ...
6
votes
3answers
130 views

Explicit use of Evaluate not behaving the way I expect it to

I discovered a strange behavior of the Evaluate function. Case 1: ...
6
votes
1answer
649 views

How is the Mathematica kernel structured internally, and how does evaluation work?

There is so much information available for Java--the internal details of (for example) the JVM memory manager are well-documented, and the performance considerations arising from its interaction with ...
6
votes
1answer
448 views

Why does Manipulate execute the expression twice?

When I execute Foobar[] in the code below and move a slider, the variable grad is printed twice. Why is this? How can I make the ...
6
votes
2answers
178 views

There is an issue with Manipulate in which it updates its argument twice in V10

I have asked this question before (here) and I thought that the issue is only when moving the Notebook window. It appears that Manipulate is working in weird manner. ...
6
votes
2answers
112 views

Showing “updating…” message while Manipulate is re-evaluating

Is it possible to show a fixed text such as "updating..." instead of the last result shown, when Manipulate is re-evaluating an expression (in a slow evaluation ...
6
votes
1answer
179 views

Machine Epsilon

I'm trying to evaluate the machine epsilon of my computer (see below). I wrote this: ...
6
votes
1answer
261 views

How to simplify expression and use HoldForm at the same time?

Hopefully a simple problem for the experts here. I have a need many times to build a symbolic expression for an equation (say a PDE) to use for plot labels in a low level function inside ...
6
votes
1answer
40 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 ...
6
votes
1answer
87 views

Debugging a $RecursionLimit error?

I sometimes encounter bugs that involve a recursion limit. It's often very hard to find the origin of the problem. Would there be a way to copy the stack somewhere and abort the evaluation in order ...
6
votes
1answer
340 views

Resume/continue interrupted evaluation

I interrupted an evaluation to quickly do something else. How do I resume the interrupted evaluation? I cannot open the "Interrupt evaluation" window, as it is disabled. There is no "Resume" button to ...
6
votes
1answer
73 views

How to reset the $ModuleNumber?

According to the documentation, we can reset $ModuleNumber to a positive machine integer. There is even an example in the doc: ...
6
votes
1answer
125 views

Comparing exact expressions for equality — is it really OK if I get wrong answer?

I found an unexpected behavior (that I think of as a bug) in evaluation of the equality operator applied to mathematical functions with exact arguments (i.e. not containing any approximate ...
6
votes
1answer
171 views

Functional-Style Partial Application and the Accumulator Pattern?

Following up on Functional-style Fixed-Length Queue Object?, I want to generalize it to a functional-style accumulator pattern. Lots of things look like accumulators, loosely defined as binary ...
6
votes
1answer
361 views

PlotStyle does not work when plotting a non-evaluated list of functions [duplicate]

When a list of functions is passed to Plot in an unevaluated form (e.g. with Through), the result is a plot with single color. ...
6
votes
1answer
649 views

Evaluate while external command is being run [duplicate]

Possible Duplicate: Computing Many Slow I/O Operations I'm launching an external command with the Mathematica front end that takes two arguments: ...
6
votes
1answer
204 views

Context “Unique to This Notebook” makes variables black even if they're not defined?

I'm trying to use this technique to keep variables separated between different notebooks. It seems to be working fine, except that variables turn black as soon as they are evaluated — any ideas why ...
5
votes
5answers
236 views

How to make a table of $\sum_{i=1}^n$?

I want to create a table of $\displaystyle \sum_{i=1}^n i^k$ for $1\le k\le 5$. The output I want to obtain is a TeXForm output as follows. \begin{align} ...
5
votes
3answers
254 views

First evaluation fails

I am fairly new to Mathematica (version 7), so please bear with me... I have duplicated, in Mathematica, a program that I originally wrote in C (it generates OEIS sequence A191837). The problem is ...
5
votes
1answer
149 views

Why does this pattern with Plus not work for numbers?

I have a very simple question about redefining basic built-in functions, such as Plus. I'm pretty sure someone must have asked a similar question around here, but I ...
5
votes
2answers
117 views

ReplaceAll performance problem: packed arrays on the LHS are unpacked when the RHS is too long

The following is one of the most mysterious performance problems I encountered and came up while extending the booleval function mentioned here. I am looking for a ...
5
votes
2answers
192 views

Remove versus ClearAll

What is the difference between Remove and ClearAll? I thought that "not being recognized by Mathematica", which is the effect ...
5
votes
1answer
107 views

“And” to continue evaluation after “False”

Below, is it possible to print No and have x be 2. That is, I'm looking for an And-like function that looks at all arguments ...
5
votes
4answers
115 views

How to map Unevaluated over a list

I have a list {a1, a2, ...... , an}, in which all as have been initialized to a number. I want to get: ...
5
votes
2answers
236 views

Associativity of `/@` [duplicate]

Why are the following not equivalent: Map[Line, Map[(Print[#]; #) &, {{{2, 1}, {1, 1}}, {{-2, 1}, {3, 1}}}]] which produces ...
5
votes
3answers
250 views

difficulty abstracting the OptionValue pattern

I am building lots of functions that use Options and OptionValue and wanted to reduce the redundancy in the expressions that ...
5
votes
2answers
67 views

Automatically scroll along with currently evaluating cell?

If I'm evaluating an entire large notebook, I usually just press Alt-V Y to find the currently evaluating cell. Is there a way to keep the currently evaluating cell automatically in focus so that the ...
5
votes
1answer
420 views

Strange Error in Bifurcation Diagram:

I am attempting to plot the bifurcation diagram of the tent map $$ f(x):=2\alpha \begin{cases} x, & 0<x<1/2\\ 1-x, &1/2<x<1, \end{cases} $$ i.e., the plot $\alpha$ vs. the limit ...
5
votes
1answer
233 views

Parts of Module body evaluated in external scope?

I have an expression that suggests that some expressions in a module body are dragging in definitions from outside the scope in a surprising way. First, consider a symbolic constant, ...
5
votes
3answers
307 views

HoldFirst and inserting additional options into a Grid of Graphics

This is related to my earlier question, but is specific to an issue I have encountered with the use of the HoldFirst First, let's create some fake data for ...
5
votes
2answers
118 views

Why does Rule behave like this?

Why does {x, x^2, x^3, a, b} /. x^n_ -> f[n] result in {x, f[2], f[3], a, b} when ...
5
votes
2answers
249 views

Why doesn't Evaluate appear to work in this RegionPlot example with MatchQ?

I am trying to plot the region over which a function of two (real) parameters a and b is real-valued, using ...
5
votes
2answers
755 views

Expression evaluation inside of FindRoot inside a Compiled Function

I'm trying to get some performance increase out of my own implicit differential equation solver using Compile[]. The uncompiled function is of the following form: ...
5
votes
3answers
640 views

Prevent Mathematica to automatically evaluate Manipulate at start

I'm using an initialization cell to import a lot of data: data = Import[myFiles]; and then I use a custom function to display this data with Manipulate: ...
5
votes
2answers
892 views

Possible to evaluate only selected cells?

Is it possible to evaluate only the selected cells programmatically that I am interested in? Say in current cell to bottom of the notebook, instead of evaluate notebook or cells?
5
votes
4answers
506 views

Delayed evaluation of assignment

I have a set of PDE's that depend on parameters. They depend on many parameters, but for simplicity we can here assume that they depend only on one, say a. I want ...
5
votes
2answers
344 views

Manipulate Evaluation Order Problem

I seem to be getting some unintended results from a nested Manipulate that I have not been able to resolve. I boiled down the problem I'm having to a simplified ...