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

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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 ...
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1answer
162 views

Force Dispatch to generate dispatch tables

Dispatch creates hash tables only for lists of length larger than 3. Is there any way to force MMA to create hash tables even for lists of length smaller than 4? ...
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1answer
154 views

how to print stack trace when TimeConstrained times out

According to the documentation, TimeConstrained generates an interrupt which interrupts the computation. This interrupt is treated just like an abort, at least in ...
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0answers
126 views

Are there any videos that show how different Mathematica expressions are evaluated?

Are there any videos that show how different Mathematica expressions are represented internally as object graphs and demonstrate how they are transformed during an evaluation? I am asking because I ...
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1answer
213 views

Strange Behavior with RegionPlot

Consider the following code. RegionPlot[Print[{x, y}], {x, -2, 2}, {y, -2, 2}, PlotPoints -> 2] ...
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3answers
185 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 ...
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3answers
153 views

Getting terms and only evaluate specific parts

I want to expand the expression but I do not want it to evaluate. Sum[(HoldForm[1/(2 # - 1) - 1/(2 # + 1)] &)[i], {i, 1, 6}] However if you evaluate this you ...
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2answers
115 views

Choosing an initializer list in With

I'm trying to have several initializer lists in a With function and choose which one I want to use. So far I have this: ...
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5answers
159 views

Using Through with SlotSequence

I have an expression consisting of a few pure functions added together like so: f+g+h I want to add the bodies of these functions together and make that a pure ...
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2answers
129 views

Simplifying expression with non-commutating entries

Say I have an expression such as (a + X)**(b-Y) where the variables above possess the following commutation relations [a, b] = [a, X] = [a, Y] = [b, X] = [b, Y] ...
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2answers
168 views

When are numerical expressions identical

Very elementary: 2 + 3 == 5 evaluates to True and 5 == 5 evaluates to ...
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4answers
982 views

Replace symbols with values without evaluation

If I have assigned values to a, b and c: ...
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2answers
278 views

How to define the irrational domain or any other arbitrary domain?

I have found no way to define the domain of Irrational numbers. I can easily define a test to see if a number is irrational by defining: ...
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1answer
326 views

mathematica does not evaluate without internet access? [closed]

I am watching the video Hands-on Start to Mathematica Basic Graphics and for about 15 minutes I was trying to evaluate $\frac{\sin x}{x}$ and each time I encountered errors like: The result can ...
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139 views

Coarse-graining in numerical integrations

I have been working recently in a coarse-graining problem I found when using NIntegrate: I am trying to evaluate the function $$f(a)=\int_0^{\infty}x\,e^{-(a^2+b^2)x^2}\text{d}x$$ numerically as a ...
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198 views
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78 views

With command does not behave as expected according to its Attributes

The attributes of the With command are HoldAll which means it should not evaluate its arguments before its starts its business. ...
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2answers
1k views

How do you configure Mathematica 9 to automatically evaluate all notebooks?

I have a Mathematica 6 course that I am using in Mathematica 9; there is no updated version. Every time I open a notebook I have to go to the Evaluation menu and click on "Evaluate Notebook". Is there ...
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1answer
498 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 ...
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2answers
92 views

Derivative before Numerical Integration

I need to take the derivative of a function that have a numerical integration on it. The variable in which the integration will be taken is not the same as the one in which the derivative will be ...
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2answers
105 views

Manipulate in modal mode

It is sometimes convenient to use Manipulate to set up global values which are to be used in the rest of the notebook. In such cases one can select and run the ...
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1answer
174 views

Can $\it{every}$ usage of While be changed into NestWhile?

Ok, I think this problem is more close to philosophy. :P I've some idea now. But I'm not sure whether it's correct. For the purpose of convenience, I will use some C-like code instead of MMA's. A ...
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2answers
146 views

Equivalent of __FILE__?

Many languages define a special identifier whose value is the path to the source file currently being processed. (For example, in C, this is done through the ...
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1answer
113 views
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1answer
131 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 ...
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3answers
223 views

How can I create a custom control which evaluates to a list of values or replacements?

I have a set of variables which are used in various places in my calculations (solving a system, initial conditions, etc.). In order to make this easier to deal with, I want to make a control-like ...
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1answer
77 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?
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1answer
133 views

Pre and Post in a Block[]

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

Append fixed value to random selection of list

(This question might be an application of this other question, but there might be another solution specific to this application that I'm not aware of.) I am currently in a situation in which (in a ...
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2answers
88 views

Parallel function evaluation for minimal value

I am asking myself, if the evaluation of a function f looking for a minimal value over a discrete set of values can be parallelize (brute scan for a potential ...
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1answer
688 views

Is there anything like a C pointer (or returning a reference) in $Mathematica$?

I want to do in Mathematica what the following does in C. ...
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1answer
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How can I save the current evaluation state of a notebook and start from it later?

I currently have a nested Table command running (in Mathematica 9), with two progress bars to track the variables. I have to shut down or hibernate the computer in ...
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1answer
160 views

Identical code, different answers?

I'm having some trouble with identical code giving different answers. On a fresh kernel (MM 9.0.0.0, Windows 64-bit), running the same code, copy-paste, gives two different answers: ...
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1answer
247 views

Assumptions seem not to be considered

In the following a,b is a probability distribution, i.e. a+b==1 with ...
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2answers
57 views

Controlling evaluation in a custom summation function

I'm doing some computations that involve summations with many indices over the same range - consider the simplified example Sum[a[i,j],{i,1,2},{j,1,2}]. To prettify ...
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1answer
48 views

How to adapt MSPToExpression function in $PrePrint?

I am introducing the mathematica Security (MSP module) to our system. The Document suggests use MSPToExpression as followed: ...
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1answer
34 views

How to evaluate following inputs only after finishing CreateDialog

I have a code which starts with the following Cell: ...
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1answer
67 views

How to define an expression which is differently evaluated in calculations and printed

Let's say, we have a list: values = {1.2, 0.04, 0.9}; Is it possible to replace 0.04 by some expression, which displays as ...
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2answers
66 views

How to print unevaluated arguments in the form they were originally typed in?

I'm looking for a way to print a function's arguments, not only unevaluated, but also in the way they were originally typed in. By way of experimentation, I tried stuff like this: ...
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1answer
157 views

ExampleData menu view

I'm trying to build an ExampleData browser, so that the "collection"/"type" is selectable in a drop down menu, and the "name" is selectable in another drop down menu. What I have so far: ...
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1answer
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What do the hashtags represent in the result of Solve, and how should I use them? [duplicate]

There is a function that I'm trying to get the inverse of. My function is a simple polynomial: Tn[T_] := 4/9 T^3/Tc^2 + 5/9 T Now I tried to find ...
4
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1answer
247 views

Is there a way to force Mathematica 8 to expand $z^{a+b}$ into $z^a z^b$?

The function PowerExpand[z^(a+b)] does not transform $z^{a+b}$ into $z^a z^b$. Is there a way to force Mathematica 8 to expand $z^{a+b}$ into $z^a z^b$? In this ...
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2answers
363 views

Overloading conjugate operator for a particular function

I trying to modify the behaviour of the built-in Conjugate[] operator on a particular function I have defined, to take into account that some of its variables are ...
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2answers
341 views

Evaluating a Recursive Expression

Why does this raise an error ...
4
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1answer
131 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] ...
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2answers
204 views

Setting a lower limit on calculation time

Sometimes it can come in handy to set a lower limit for a calculation. Consider for example an animation that is generated by some infinite loop, which would run way too fast to display properly for ...
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1answer
149 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 ...
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1answer
94 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: ...
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1answer
897 views

Behavior of expression evaluation in Plot

I'm confused with Mathematica's way of parsing expressions. I've been struggling with this for a while and never found an exhaustive answer, sometimes things don't parse the way I think they would ...
4
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1answer
146 views

How can I test properties of a symbol without unwanted evaluation

Problem How to get the head, size, dimensions, etc. of a symbol without evaluating it? Since Mathematica does not allocate fix storage space and type to symbols it is not trivial to query runtime ...