Tagged Questions

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

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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
291 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
200 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
176 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
434 views

Unique[] symbol not properly tracked

In a nutshell, why does this work (change y and see how the value updates) ...
5
votes
1answer
228 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
285 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
311 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
360 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
107 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
2k 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
530 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
344 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
895 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 ...
12
votes
4answers
487 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
458 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
302 views

Why do I have to put Evaluate[] here

I wanted to draw some contours. I succeeded with this: ...
5
votes
3answers
248 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
492 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
144 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
220 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 ...
0
votes
1answer
111 views

NIntegrate failling on floating value

I'm trying to take the following integral NIntegrate[ ((Sin[Q 1]-Q 1*Cos[Q 1])/(Q 1)^3)^2 * S[Q,0.4,2] * Q BesselJ[0,0.5Q] , {Q,0,Infinity}] ...
7
votes
2answers
171 views

“A number in base b” and pure functions: why doesn't b^^# & work?

Why do the following not work (in Mathematica 7)? 2^^ # & /@ {1000, 1101} and 2^^ # & @ 1101 This does work: ...
6
votes
2answers
461 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 ...
4
votes
1answer
207 views

Assumptions seem not to be considered

In the following a,b is a probability distribution, i.e. a+b==1 with ...
11
votes
7answers
325 views

Question about evaluation control

I want to make a function that takes a function as a parameter and prints an integral with the function inside. I've tried this: ...
6
votes
4answers
375 views

Attaching persistent assumptions to symbol definition

Is it possible to attach assumptions to a symbol? This relates to this question. Most of my work involves physical equations, i.e. there are basic assumptions on variables that will always hold true ...
10
votes
2answers
512 views

DSolve cannot solve for certain branches of the solution

Update - This has been fixed in 10.0.0 Could somebody please tell me, why I am always getting an error message when trying to run the following code: ...
5
votes
2answers
222 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 ...
4
votes
4answers
4k views

Mapping multiple parameters of a function to specific values

I am a little bit confused by the documentation for Apply (@@). I want to define a list of parameters, for instance: ...
5
votes
2answers
666 views

Speeding up mathematica by subsitituting numerical values

According to this Wolfram Blog post, one can speed up Mathematica code by substituting numerical values as soon as possible. How does one substitute before the main expression is evaluated? The ...
9
votes
2answers
154 views

A notebook created on demand from a main document showing executable input along with output cells

I would like to make Mathematica documents with hidden calculations, such that they can be visualized on demand. In general it can be done in several forms and I actually use some. I would like to ask ...
10
votes
2answers
253 views

Make a button that evaluates a function over and over

I would like to have a command "RedoButton" which would make a button (or whatever control is suitable) that when clicked would print the value of a certain function over and over in the same place. ...
10
votes
2answers
314 views

Unexpected differences with various uses of NormFunction

I would expect all of the following to give the same answer (2.12467) but only half of them give this answer. The others seem to be using the default ...
11
votes
3answers
254 views

Numbers in alternate bases transcend the evaluator?

It looks to me like a number in a base other than base 10 gets evaluated before the evaluator ever gets a chance to be tweaked. For example, FullForm[16^^abcdef] ...
4
votes
1answer
382 views

Can a Table iterator “leak” into a Module?

I want to repeatedly call a module by using a Table statement. When I use an i iterator in the Table command calling the module, I receive the error message ...
17
votes
3answers
566 views

How can I completely ban usage of some functions in output and mandate use of others?

For example, I hate that Mathematica uses Pochhammer symbol in outputs and prefer all the expressions in Gamma function. How can ...
3
votes
1answer
256 views

FunctionInterpolation Errors / Question re Evaluation Order and Options

I have using Mathematica functions that takes a Cartesian coordinate relative to the Earth (xyz) and converts it to a latitude, longitude, and altitude (lla). And here it is: ...
7
votes
4answers
1k views

Force function to make assumptions about its input variables in Mathematica

I'm trying to force a Mathematica function to make an assumption about its input variables. In my case, I'm trying to define a function to return the pdf of a Gaussian. But let's use a simple toy ...
5
votes
2answers
677 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: ...
4
votes
3answers
371 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 ...
6
votes
1answer
189 views

Difficulty catching thrown errors in asynchronous tasks

In this Question, Leonid explained that module variables can get garbage collected from a chain of asynchronous tasks unless their Temporary attribute is cleared ...
6
votes
1answer
241 views

Module variable scoping in Scheduled Tasks?

I ran across a scoping puzzle while experimenting with ScheduledTasks, and I'd be grateful for an explanation from the sages here. I found a workaround by intuitive horse sense, but was unable to ...
5
votes
1answer
119 views

Changes in Handling of Real Zeros

I recently upgraded from Mathematica 5 to Mathematica 8 and I have a number of notebooks that no longer work correctly. The problems relate to the use of units. I don't need complicated unit ...
7
votes
1answer
212 views

How do I write a ValueQ function that only returns True if there exists an OwnValue?

Reading the comments in this answer has motivated me to request a full solution to part of this problem. What I'd like is an efficient solution that returns True ...
12
votes
3answers
328 views

Arguments to If[] are not evaluated

I got bitten by the following: f[x_] := 3*x; g[x_] := If[Log[f[x]] < 0, f[x], 0]; g[x] Out[11]= If[Log[3 x] < 0, f[x], 0] where I thought the call to ...
8
votes
1answer
481 views

How to properly DumpSave & Get Global`s symbols inside packages while not touching Global context?

For efficiency reasons I prefer to use DumpSave instead of Save. For ease of access I prefer to save symbols in ...
11
votes
1answer
249 views

Old values are not freed/garbage collected when you re-evaluate an assignment

For this code: (* Cell 1 *) generate := Module[{x}, x = Range[100 * 1000 * 1000]; x]; (* Cell 2 *) g = generate[]; MemoryInUse[] If I evaluate cell 2 ...