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

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5
votes
5answers
636 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 (...
8
votes
1answer
130 views

Prevent Plus from threading InterpolatingFunction

For an InterpolatingFunction $y:\ \mathbb{R}\to\mathbb{R}^2$, Plus is unaware of this, so when I do any modifications to it in ...
2
votes
2answers
161 views

Updating a tracked symbol inside Refresh?

I have some code inside a Manipulate, whose goal is to allow the user to edit the upper half of the matrix while keeping it symmetric at all time. The minimal code ...
5
votes
2answers
5k views

Simple ways to evaluate a derivative at a point?

The contrast in behavior between, say, f[x_] = Sin[x^2]; f'[2] vs. u[x_, y_] = Cos[x + y^2]; has always bothered my ...
14
votes
2answers
258 views

How can I access a variable in one evaluator from another evaluator?

I have two notebooks, each with a different kernel. Is there a way to grab the value of a variable in KernelA from KernelB?
16
votes
2answers
1k views

Difference between AbsoluteTiming and Timing

I need to evaluate the efficiency of my code. Therefore I would like to evaluate the time the code need for some calculations. Mathematica gives me two possibilities for this kind of evaluation: ...
11
votes
3answers
525 views

Labeling plots without evaluation

This is my first question here so please excuse my mistakes. Let us consider a rather contrived example: ...
2
votes
1answer
128 views

Implementing a For (?) or series or loop (?) for individual results for every x to n

I'm working on improving a modeling formula and have spreadsheets worth of data to use, but my work so far has been quite tedious. I'm essentially pulling 20 rows of data from each separate sheet of a ...
4
votes
2answers
662 views

How to make a function that evaluates an expression?

I'm trying to make a function where the input is an expression, but somehow it just won't be evaluated. For example, this little function doesn't work: ...
5
votes
1answer
379 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
0answers
157 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 ...
4
votes
1answer
67 views

How can I kill one evaluator from another?

I have a kernel named A in one notebook and other notebook with kernel B, how can I kill B from A?
6
votes
1answer
575 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: ...
4
votes
1answer
127 views

Pre and Post in a Block[]

Why does Block[{$Pre = ( 1 + #) &}, 1] produce 1 while ...
12
votes
2answers
423 views

Preventing Numerical value from being evaluated

I have searched stackoverflow (and comparable pages) for quite a while now (got redirected from there to this specialized stack), and I surrender. I am trying to evaluate an expression that is small ...
7
votes
1answer
189 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 ...
15
votes
1answer
422 views

Using Evaluate and Evaluated -> True in Plot

A few use cases: (1) This, as expected, returns (almost) immediately: f[x_?NumericQ] := Evaluate[(Pause[1]; x)] Plot[f[x], {x, 0, 1}] (2) This takes ...
1
vote
1answer
179 views

Skip one step of the loop if there is an NIntegrate::eincr message

Is there a possibility of skipping one step of a loop if in this step there appears an error like NIntegrate::eincr? After skipping, the loop should go to the next ...
0
votes
1answer
67 views

How can I restrict a notebook to evaluate only if I am user 'root'?

I am playing with openCL on Linux with an AMD gpu, and due to a glitch in the driver, I need to be 'root' to get stuff to work. Installation question here.
11
votes
2answers
255 views

can a ColorFunction have side effects?

Can anyone explain this (to me) odd behavior. If I run this code once (fresh kernel) it works as intended. ...
13
votes
5answers
720 views

How are parameters evaluated for a Plot in Manipulate

I am trying to get my head around how Manipulate evaluates functions in a Plot. I have read the introduction to Manipulate, and introduction to Dynamic, but I still ...
1
vote
2answers
145 views

How can define a set of nested parameters

I would like to know how I to define a function with a nested set of parameters (or whatever you would like to call it). For example, how would I get the following function ...
5
votes
3answers
248 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 ...
7
votes
2answers
211 views

Why does the name of a pattern affect the result of a transformation rule?

I was playing a little dirty, trying to get a template for defining a Curl[] operator. I wrote the following rule, which I knew was going to spit out a few ...
13
votes
1answer
331 views

Evaluation indicator for a notebook

I have a GUI with a number of TabView and other Manipulate controls. Sometimes clicking from one tab view to the other can take ...
1
vote
2answers
100 views

What is the default file path used by the Put function and how do I pre-evaluate an expression to use in Put?

I have a problem of trying to store some output in an external file. In one note book I define a function f[x_]:=AdvancedCalculation, where this function generates ...
0
votes
1answer
136 views

Slow Dynamic Button Does Not Print [duplicate]

Possible Duplicate: Why do buttons with ChoiceDialog freeze the front end? Why is SystemDialogInput failing to return a save file path? Evaluation inside Button stops after some seconds I ...
4
votes
1answer
129 views

Tweaking Prime[n] to return 1 when n==0

I manually evaluate this cell to set Prime[0] Unprotect[Prime] Prime[0] = 1 Protect[Prime] I manually evaluate this cell to reset Prime[0] ...
13
votes
2answers
296 views

How to make use of NumericQ[x] = True (and use it safely)?

Basic Issue: I'm trying to understand the proper use of NumericQ's "magical" capabilities. Please consider the examples below. Actual question and some links are ...
1
vote
1answer
214 views

Particular solutions of a Differential Equation not evaluated in a given case

Below first case which gives particular solutions of an OED correctly: ...
7
votes
2answers
177 views

Keywords to find documentation for this syntax

Mathematica allows this syntax, but I cannot find any documentation (or books) that discuss the various uses/advantages of it ...
13
votes
1answer
437 views

Unique[] symbol not properly tracked

In a nutshell, why does this work (change y and see how the value updates) ...
5
votes
1answer
231 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, ...
15
votes
1answer
293 views

Polynomial expectations of generic distributions

Summary Polynomial expectations depend only moments and cross moments of a multivariate distribution. I would like to use Expectation to compute polynomial ...
2
votes
2answers
1k views

Animation of Differential Equations from NDSolve with ParametricPlot3D and Evaluate

I have a system of differential equations (referred to as "s") and use NDSolve to obtain the solution. I substitute the interpolated functions for the original ...
10
votes
3answers
1k views

All curves in plot have the same style. Cannot be fixed with Evaluate[]

Usually, when I plot multiple curves in Mathematica Plot[{x,x^2,x^3},{x,0,1}] they are given different colors. However, if I try to construct a list inside the ...
10
votes
3answers
318 views

How can I hold UpValues but evaluate other expressions?

Consider these definitions: own = "OwnValue"; down[_] = "DownValue"; sub[_][_] = "SubValue"; N[n] = 3.14; _[___, up, ___] ^= "UpValue"; The attribute ...
6
votes
1answer
376 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 ...
3
votes
2answers
109 views

Turning evaluation off

I am making a directed graph, but Mathematica keeps trying to evaluate my labels. I know that I can just use " ", but I have a lot of input. Is there a way to turn evaluation off? ...
2
votes
1answer
3k views

setting a variable equal to the output of FindRoot

So I set a function f[x] f[x_] := x*E^(-x) - 0.16064 Then I set a variable 'actualroot' to the function FindRoot, starting at 3 ...
14
votes
4answers
554 views

Returning an unevaluated expression with values substituted in

Let's say I have a function formula[x_List] := (x[[1]] - x[[2]]) + (x[[3]] - x[[4]]); and I want to pass it a variable and get back the unevaluated formula with ...
3
votes
3answers
361 views

Help on evaluation control?

I want to plot series of slopes: x, 2x, 3x, 4x, 5x, 6x... I'm trying to do this: ...
20
votes
2answers
910 views

Mathematica for Computer Scientists

Background I've coded in C/Scheme for 10 years. I have a BS CS. I've recently become very interested in pattern-matching (lisp's match macro), and term rewriting systems, which brought me to ...
15
votes
4answers
543 views

Recovering intermediate results from a Table after an interruption

I am interested in knowing if it is possible to recover intermediate results from a Table after an interruption. Let us say I want to produce a really useful table ...
5
votes
2answers
513 views

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

Let us say I want to show how the Taylor's series for Sin behaves: ...
8
votes
2answers
319 views

Why do I have to put Evaluate[] here

I wanted to draw some contours. I succeeded with this: ...
5
votes
3answers
253 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 ...
15
votes
1answer
502 views

Wagner's trick to monitor FindRoot no longer works in Mathematica version 8

I recently learned that we can use Print as a monitoring tool. My favorite is Ted Ersek's example ...
3
votes
1answer
146 views

Set promotes Rule to RuleDelayed?

In mentally building a model of how Mathematica works, I naively expected Set to create a Rule in a symbol's ...
9
votes
4answers
224 views

Leave expression tree formatting the same when a replacement rule is applied

If I type e1 := 3 x + 2 (1 + y) z // TreeForm, I get an expression tree. If I then type e1 /. x -> 3, I get another ...