# Tagged Questions

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

2k views

### Can Mathematica do two evaluations at the same time?

When one evaluation is running, if I want do another evaluation, Mathematica will put the second one in the queue and run it after the first evaluation finish. However, the first evaluation may take ...
74 views

### Apply a function to the current selection in place

Say a have the function foo: foo[x_] := x + 2 Like the Evalution ...
610 views

### How do I get Mathematica to return a function call unevaluated?

How do I get Mathematica to return a function call (conditionally) unevaluated? I expect this may use the slightly-mysterious Hold function. As a toy example, ...
97 views

### Simplifying Fourier transform of a complicated function

I would like to evaluate the following expression but takes too much time. I would be greatly appreciate for any comments to make it fast. ...
45 views

### can I evaluate multiple cells at the same time? [duplicate]

my laptop has 2 cores, can I assign a core to evaluate one code, and the other core for another code in parallel instead of evaluating in sequence? thanks
81 views

### Optimizing repeated function calls

Easiest way to keep my library nice, is to naively call some functions many times with same parameters. Doing so prevents from zoo of (library-)global variables and complicated initialisation ...
105 views

### Defer parts of the expression

Is there a way to Defer only parts of the expression? For example, I have a=1; and then I want the expression to be shown as...
144 views

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

I discovered a strange behavior of the Evaluate function. Case 1: ...
148 views

### Symbolic integral including Hermite polynomial does not evaluate

I am trying to evaluate the following integral: Integrate[HermiteH[n, Sqrt[a]* x] * Exp[- (c/2)* (x^2 + y^2) + b* x * y - (a * x^2)/2], {x, - Infinity, Infinity}] ...
154 views

### Why even try the semantic constraints, if expression can't match the pattern structure?

This result is unexpected: Trace[MatchQ[{7}, {_?NumberQ, __}], NumberQ] (* -> {{NumberQ[7], True}} *) Why evaluate NumberQ...
177 views

### Getting unevaluated function expression

Say I've got a function f[x_] := a x^2 + b*x + c; and later set for some other reason a=1; how can I get the expression of f in ...
137 views

### Handling a sequence of unevaluated arguments

I have the following piece of code: ...
212 views

### Wrapping at evaluation for inline cell

I've been playing with inline evaluation and I've came to the conclusion that it's most convenient to put the Dynamic@ inside the inline cell, so I've started to ...
133 views

### Example from Mathematica documentation (ExtremeValueDistribution) seems to be evualting “forever”

I am referring to this example at the reference page for the extreme value distribution: http://reference.wolfram.com/mathematica/ref/ExtremeValueDistribution.html#6764486 The first three commands ...
154 views

### Time delayed evaluation of a function

I'd like to write a function that delays the evaluation of a function (say) $5$ seconds after I hit Shift+Return. Is this possible?
559 views

### Why is evaluation Enter for Mac and shift+Enter for Windows? [closed]

Per the title, why is evaluation done using just the Enter key for Macintosh and shift+Enter for Windows? UPDATE Okay, I see the Mac keyboard's "Enter" key is actually labeled "Return", so by Enter ...
32 views

### How to Plot a function that returns multiple values? [duplicate]

I have a function that returns multiple values, like this: f[x_] := ( (*... something ... *); {y1, y2}); They are computed together, so there's absolutely no ...
61 views

The problem is Find two linearly independent solutions of $2x^2y'' -xy' + (-4 x + 1)y = 0, \, x>0$ of the form $y_1 = x^{r_1}(1 + a_1 x + a_2 x^2 + a_3 x^3 + \cdots)$ and $y_2 = x^{r_2}(1 + b_1 x ... 2answers 327 views ### Expectation of a family of random variables I did some search here, but seems that no one asked about this. I want to define a family of independent and identically distributed random variables,$x_1,...,x_n$, and then calculates the expected ... 1answer 112 views ### What is “ (Dialog) Input [ ] := ” after evaluating a cell? I have done a time-consuming run and calculation. After many hours ( about 7 hours!), the black color which shows that the cell is evaluating, turn into gray and a strange text appears like this : <... 2answers 1k views ### Nothing appears in simple plot I'm trying to get the following simple code to work. (The code is just supposed to graph the norm of the second derivative of a vector function). ... 1answer 691 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 ... 3answers 242 views ### Graphics in Notebook Different from Graphics Expression? Consider the expression TreeForm[a+b^2+c^3+d] which displays as This is a nice Graphics object, as I can prove by typing ... 1answer 135 views ### Why does evaluating an integral within a Plot expression take so long? [duplicate] I want to evaluate Plot[Integrate[Sin[((1 + 1/2) x)] (1/(2 Sin[(x/2)]) - 1/x), {x, 0, t}], {t, 0, 5}] but it takes ages to load on Corei3 computer with ... 2answers 250 views ### Half-delayed evaluation In a certain wider context, I need to make some delayed definitions, such as x := a + b + c, but within these definitions I want ... 0answers 35 views ### RandomReal behavior in Block environment [duplicate] I ran into an unexpected behavior of RandomReal function inside the Block environment. If I simplify my problem: I wanted to use two random local variables, such that the second one would be less that ... 0answers 40 views ### Notification when evaluation completes [duplicate] I thought it would be fun to see a list of ways to have Mathematica notify you when a long evaluation completes. There are a few posts up already that address specific methods, given below, but not ... 2answers 2k views ### How to evaluate Modules in a notebook from another notebook? I would like to create a notebook populated with several modules and be able to evaluate these modules by running a separate notebook. I have attempted several uses of the ... 0answers 39 views ### Number precision in a list [duplicate] I have list with elements: ... 1answer 104 views ### Evaluate integral of a series I want to evaluate this integral, but it won't work. Does anyone knows why? ... 2answers 85 views ### Can I have Mathematica show intermediate forms before final evaluation? If I have x = 2 and I want to evaluate y = x^2 I would like to the output to show ... 0answers 100 views ### How to modify the file “KeyEventTranslations.tr” to use Enter to evaluate the current cell? [duplicate] I asked the following question before, but I do not think it has been fully answered. By default, we use Shift+Enter to evaluate the current cell, and use Enter to get a new line. Is there a way ... 2answers 84 views ### Extract the real components from a very large expression Suppose I have a very long expression (>500,000 characters) which contains a mixture of real and imaginary terms. e.g ... 1answer 252 views ### new kernel for notebook I know I can create a new kernel for my notebook from the evaluation menu but is there a command for this? I'd really like some of my notebooks to startup their own kernel as the first line of code. 1answer 41 views ### is there a way to construct a pattern that would trigger when an expression is used as a held/unevaluated in some form? For example, consider the following code f[x_] := (Print["evaluated f"]; workWith[x]); We use it, then f evaluates: ... 1answer 250 views ### Nested Derivative These two expressions are mathematically the same, but when substituting with the same rule, yield different results. What is happening? ... 2answers 270 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; tempx = 6; Begin["temp"]; {x, Globalx} The ... 2answers 2k views ### Integrating a Simple Piecewise Function If I define f[x_]:=If[x<0,-1,1] and then integrate,say Integrate[f[x],{x,-3,7}] I get what I expect, namely 4. But ... 5answers 496 views ### Result about Context is inconsistent with the description of “Power Programming with Mathematica” x = 5; tempx = 6; Begin["temp"] {x, Globalx, temp`x} The result in my Mathematica session is {5,5,6}, but it's ... 1answer 97 views ### Where do Mathematica's probability functions draw a line in the sand for predicates? Thinking about a recent question mis-posted here (belonged on math), I noted the following. A contrived example - probability that a or b are 1: ... 1answer 290 views ### Why does Plot[Hold[x], {x,0,1}] work? It appears that, counter to my expectation, all of these (and probably many others) seem to work fine: ... 0answers 81 views ### Assign a value to a variable without using Set or SetDelayed? I supose probably yes, but at the end I assume that internally mathematica has to use Set or SetDelayed. Am I right? Background: I am developing a super simple phraser that takes a code description ... 2answers 129 views ### Merging two held expressions into a held compound expression Consider e1 = Hold[a = x + x; b = y + y + y]; e2 = Hold[c = a + a + b + b + b; c^2]; How can I obtain the following? ... 1answer 84 views ### Commutative algebra by generators and quadratic relations My apologies if this has been asked before. Please also be gentle, as this is my first question here. I am trying to define a commutative algebra by generators and relations in the following way. ... 2answers 183 views ### Stopping a head from evaluating more than once While attempting to answer my own question, Is there a way to "hold" prefix / infix / postfix notation?, I came across the need to evaluate a recursive function only one level deep. For ... 2answers 162 views ### Why the Block command does not forget the$ContextPath variable

I do not understand this behavior: ...
324 views

### How to see which arguments are passed into a function

It is often that one wonders which arguments are evaluated before being passed into a function. I would like to know if it is possible to see which argumets are being passed into a function without ...
371 views

### Replacing parts of a held expression with held parts of another expression

I'm applying the Trott-Strzebonski technique in order to replace inside a held expression. ...