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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1
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1answer
103 views

FindRoot with vector functions

I'm trying to solve a system of non-linear equations with FindRoot, and I get the answer, but also a ...
0
votes
1answer
172 views

How does Mathematica interpret a expression?

I'm a beginner to Mathematica. I'd read several document. But I still have a problem. For example, every expression in Mathematica are of the form ...
2
votes
0answers
42 views

Timing of ParallelDo versus Do: simple example [duplicate]

I'm trying to understand why a simple do-loop takes substantially longer when done in parallel than sequentially: ...
2
votes
1answer
89 views

ParallelEvaluate: Evaluation Rules and Increment

I'm trying to understand how ParallelEvaluate works, considering the two following snippets: ...
0
votes
3answers
69 views

Automatically evaluate next cell

I am new to Mathematica. I am trying to achieve the following: I need one input cell in which I set parameters, then another input cell where functions are defined and calculations are performed. ...
3
votes
1answer
59 views

Print prints into the Messages notebook rather than into the evaluation notebook

Some time ago I noticed that the results of the evaluating the function Print[something] does not emerge in a new cell created in the notebook where the operation ...
3
votes
3answers
174 views

will the same result be evaluated twice per evaluation?

here is the silly question of mine, if mathematica takes 3 seconds to evaluate the function ...
1
vote
0answers
79 views

Expression for evaluating multiple functions?

I am constructing 3D data points for a plot and corresponding to specific conditions "manually". I define the values of five parameters [these I always have to define myself]. From those, I evaluate ...
0
votes
1answer
44 views

Resolving Error: Mathematica evaluation order on Lists

I have a table that is 27 x 27, each entry corresponds to an element from the periodic table. I use the replacement rules in element list to allow me to convert a list of elements into a list of ...
0
votes
4answers
147 views

Minimization in single component of BSpline to extract points

I smoothed some data with a BSpline $B[t] = (x[t],y[t])$. I would like to extract certain points from this spline by their x-Values, $x_0$. The easiest way I came up with was to minimize ...
1
vote
2answers
59 views

Pattern matching to head with HoldFirst

I want to define a function that only operates on expressions with a head from a given list, such as f[expr:(_And|_Or)] := Print["LHS is ", expr[[1]]]; This of ...
4
votes
3answers
3k views

How to force 2+2=5

I was looking at this question (writing a program such that 2 + 2 = 5) and tried to write something in Mathematica, but I couldn't get something to work without completely replacing ...
6
votes
1answer
126 views

Machine Epsilon

I'm trying to evaluate the machine epsilon of my computer (see below). I wrote this: ...
5
votes
2answers
93 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 ...
0
votes
0answers
44 views

Scoping problem with Manipulate [duplicate]

Consider the following simple code: f = Sin[a x]; Manipulate[ Plot[f, {x, 0, 10}], {a, 0, 10}] Manipulate takes f to be ...
3
votes
1answer
84 views

How to localize symbols on the right-hand side of Rule when using ReplaceAll?

I am frustrated by the following: {1, 2, 3.0} /. a_Integer -> a + 1 The a on the left side of the arrow is localized and ...
8
votes
2answers
163 views

How to correct this, `f[a_] := FindRoot[eq == 0, {x, 0.5}]`, where `eq` contains a parameter $a$, without using `eq[a]`?

I want to solve an equation with a parameter $a$, and define the result as a function of $a$. It is something like this: ...
6
votes
1answer
152 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 ...
3
votes
1answer
46 views

Apply a function to the current selection in place

Say a have the function foo: foo[x_] := x + 2 Like the Evalution ...
10
votes
2answers
360 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, ...
0
votes
2answers
70 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. ...
1
vote
0answers
38 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
0
votes
1answer
55 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 ...
2
votes
1answer
72 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...
6
votes
3answers
109 views

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

I discovered a strange behavior of the Evaluate function. Case 1: ...
0
votes
1answer
76 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}] ...
3
votes
1answer
127 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 ...
0
votes
1answer
101 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 ...
2
votes
2answers
96 views

Handling a sequence of unevaluated arguments

I have the following piece of code: ...
2
votes
1answer
102 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 ...
4
votes
1answer
124 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 ...
2
votes
2answers
127 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?
1
vote
1answer
189 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 ...
1
vote
0answers
30 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 ...
0
votes
2answers
55 views

Evaluate differentiation after replacement

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 ...
2
votes
2answers
187 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 ...
2
votes
0answers
51 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 : ...
0
votes
0answers
50 views

Numeric function not fully evaluating

I'm running into an issue where it seems Mathematica is not fully evaluating the output of my function h[t_]. I included the definition of phi[t_] just to demonstrate that it is a numerically defined ...
7
votes
2answers
196 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). ...
5
votes
1answer
191 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 ...
7
votes
3answers
216 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 ...
0
votes
1answer
97 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 ...
8
votes
2answers
137 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 ...
0
votes
0answers
30 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 ...
0
votes
0answers
39 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 ...
1
vote
2answers
187 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 ...
0
votes
0answers
36 views

Number precision in a list [duplicate]

I have list with elements: ...
0
votes
1answer
96 views

Evaluate integral of a series

I want to evaluate this integral, but it won't work. Does anyone knows why? ...
2
votes
2answers
73 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 ...
0
votes
0answers
96 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 ...