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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Apply a function to the current selection in place

Say a have the function foo: foo[x_] := x + 2 Like the Evalution ...
609 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
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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 ...
104 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...
175 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 ...
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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 ...
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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 687 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 250 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: ...
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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. ...
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Cell seems to be evaluating in exponential time even though it shouldn't

I am trying to implement Newton's method for a given function f[x] and a starting x-value xval. The code should print out each new x-value as it approaches one of the zeroes of the functions. g[x] is ...