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

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0answers
46 views

Optimization for iterating and plotting a matrix product and its elements?

I have an iterative matrix product of this type Since i didnt knew how to do it, I explicitly wrote the product as {Ayn + Bxn, Cyn + Dxn} and evaluated it with the NestList construct ...
2
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0answers
44 views

Executing selected code [duplicate]

In current Mathematica interface, if I select some piece of code and press CMD + Shift + Enter, the code is evaluated in place. Replacing the selected part by the evaluated version. The question is: ...
2
votes
0answers
43 views

Find the numerator of 6/8 [duplicate]

The statement Numerator[6/8] evaluates to 3. Numerator[Hold[6/8] does not work. What function NewNumerator[6/8] evaluates to 6?
2
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0answers
52 views

Import names into notebook namespace [duplicate]

I have function that at some point has list of strings (e.g. {"apple","pear"}) and I want to declare (initialize) those variables in notebook namespace to default ...
2
votes
0answers
414 views

Mathematica shift-enter problem [closed]

Would really appreciate if someone can help with this problem: When I first open a Mathematica note book, say you do 1+2 and press shift-enter. As expected, I get "3" as the output. Now suppose you ...
2
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0answers
71 views

$Epilog does not work when exit

The following code does work: $Epilog := Print@1; Quit[]; But if I close the document and exit WM or click QuitKernel, it does not work. Why?
2
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0answers
54 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
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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 ...
2
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0answers
530 views

Lazy evaluation/loading of parts of an expression

Is it possible to have an expression x such that its elements are only evaluated when they are individually accessed, for example when evaluating statements like <...
2
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0answers
120 views

Strange double evaluation using MorphologicalGraph

(MMA 9.0.0 on Mac OS/X 10.8) Please consider the following snippet (this is as SMALL as I could make it -- my attempts at making a smaller repro-case eliminated the effect that I am investigating) <...
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vote
5answers
179 views

Do not expand matrices in Mathematica calculation

Here is an example of a problem I'm having. Consider that I have defined: omega={{p[t]},{q[t]},{r[t]}} x={{a},{b},{c}} R={{1,2,3},{4,5,6},{7,8,d}} What I would ...
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2answers
124 views

NIntegrate evaluates its 1st argument while it has the attribute HoldAll?

NIntegrate owns the attribute HoldAll: Attributes@NIntegrate (* {HoldAll, Protected} *) ...
1
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2answers
80 views

Evaluating and Plotting Multiple Zero-Counting Functions

In work that I am doing, I am trying to plot multiple zero-counting functions, depending on how a parameter works. For example, if the zeros of one function are {1, 2, 3, 4, 5, 6, 7}, the zeros of ...
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2answers
291 views

How can I speed up this plot manipulation? Why does Evaluate not help?

If I were able to "Save" the computed inverse function somewhere and then plot it, the manipulation would become faster. As I understand, Evaluate should do the job, but for some reason it does not. ...
1
vote
3answers
102 views

Keep leading/trailing zeroes (like Defer except with numbers) in a given number

I'm trying to write a function that counts the number of significant figures a given number has so I can ensure my calculations are rounded correctly; however, I am having a lot of trouble preventing ...
1
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3answers
64 views

Controlling the evaluation of other arguments in pure functions [duplicate]

I have a piece of code where I would like to do the something like the following: ...
1
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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 ...
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2answers
157 views

Evaluation of elements in a list and then sorting them

This is probably a simple problem, but I'm having a lot of issues with it because I'm unfamiliar with Mathematica syntax. I have a list ...
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2answers
170 views

Why does Evaluate[a[[1]]]=0 assign a value to a variable while a[[1]]=0 doesn't?

I'm trying to do a small page counter with Mathematica, for leting me know about my reading progress on some books. I'm stuck on a problem: ...
1
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2answers
110 views

What is the default file path used by the Put function and how do I pre-evaluate an expression to use in Put?

I have a problem of trying to store some output in an external file. In one note book I define a function f[x_]:=AdvancedCalculation, where this function generates ...
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3answers
144 views

Multiple Plots inside a Manipulate with different dynamic variables on their x-axes

I have an expression with lots of variables, and I would like to make several plots of the expression, where the axis in each is a different variable. The idea is to put them side by side inside a <...
1
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2answers
208 views

Evaluate a list

I have a function $f(x_1,\cdots,x_n)$ that takes $n$ arguments, and I would like to evaluate it using a list of lists $\lbrace\lbrace x_1,\cdots,x_n \rbrace,\cdots,\lbrace x_1',\cdots,x_n' \rbrace,\...
1
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3answers
137 views

How I create a 'TraditionalForm' expression in which only parts are evaluated?

I have an expression for the form Subscript[W, f[a, b]][c] = ρ^f[a,b]ω[c]ρ^-f[a,b] that I want to render in TraditionalForm ...
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2answers
136 views

Automatically evaluating related cells

I have the cells: In[1]:= l = 2 + 2; In[2]:= l >= 5 After evaluating them: Out[2]:= False Is there a way to evaluate ...
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1answer
68 views

How to force evaluation inside the body of a pure function?

For example, I'm writing a function to scale my list of numbers into a specific range. It goes like ...
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2answers
60 views

Unpacking NumberForm expressions

Given a NumberForm expression, e.g.: NumberForm[N[Pi], 10] How does one get the underlying numerical expression (short of ...
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2answers
154 views

After NumberForm I cannot apply a Sine function. Why?

After NumberForm I cannot apply a Sine function. Why? This works: sol1 = x /. Solve[x^2 - 3 == 0, x] Sin[sol1] Output = $\{-Sin[\sqrt{3}],Sin[\sqrt{3}]\}$ Also ...
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vote
2answers
276 views

How to get the absolute difference between two angles

I need a function that will give me the shortest separation between angles that range from -pi to pi. For example if I have two angles 3pi/4 and -3pi/4, I would like a function that will tell me pi/2 ...
1
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1answer
375 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 ...
1
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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 ...
1
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1answer
224 views

Passing a joined list of symbols for Module or Block to treat as its own local symbols

The Question I'd like to write a function which itself takes a list of symbols, e.g. Foo[{x, y, z}] to pass to Module within,...
1
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1answer
89 views

How can I draw truth tables using Mathematica [duplicate]

For instance, the given expression p ⊕ (p v q) In the problem I'm trying to solve. There's a Mathematica answer to this: ...
1
vote
1answer
133 views

Why isn't Mathematica reducing my result to a number? [closed]

I do not understad why the program do not show the number values. Even when I use N[xx]. How can I simplify this?
1
vote
1answer
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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2answers
61 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 ...
1
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2answers
635 views

Converting expression into string without evaluating it

How can one convert a Mathematica expression into a string without the expression being evaluated first? I tried using Hold, but it returns ...
1
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1answer
663 views

Forcing evaluation of ArgMax

How to force evaluation of ArgMax before its output gets used in Solve? Background: I'm trying to solve for the Nash ...
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2answers
171 views

How can define a set of nested parameters

I would like to know how I to define a function with a nested set of parameters (or whatever you would like to call it). For example, how would I get the following function ...
1
vote
1answer
119 views

Evaluate multiple notebooks sequentially and automatically

I know how to run multiple notebooks at once. But my problem is that due to the RAM capacity, I have to run these notebooks consecutively. Another problem is that since I may not be in my office all ...
1
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1answer
49 views

problem about Root and Hypergeometric2F1

See these example, why does the output is different? ...
1
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1answer
55 views

How to achieve fun[Unevaluated[f][Unevaluated[x], Unevaluated[y]] in a more elegant way?

I have defined a function fun[f_[x_,y_]]. When I call it, I want to wrap everything by Unevaluated: ...
1
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1answer
83 views

Replace symbols in output without evaluation

I found the Wolfram example for ExpandNCM but I want a more human-readable output form. I want to evaluate ExpandNCM, for example with ...
1
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1answer
81 views

A With and ContourPlot difficulty

Consider: sys = {u (1 - u + a v), r v (1 - v + b u)}; With[{a = 2, b = 3, r = 1}, Evaluate[Thread[sys == {0, 0}]]] Which gives the output: ...
1
vote
2answers
90 views

Assigning to the “local” version of a symbol

Compare Manipulate[c[1] = 1; c[1], {c[1], 0, 1}] with Manipulate[Do[c[i] = 1, {i, 1}]; c[1], {c[1], 0, 1}] The first case ...
1
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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 ...
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1answer
44 views

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 ...
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1answer
141 views
1
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1answer
187 views

direct assignment to the element in a Table

I have already asked a related question here why set values in this way doesn't work? But I think I have to write the question which I encountered explicitly? ...
1
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2answers
50 views

Chains of approximate numeric equalities

Mathematica considers two numbers equal if "at most their last seven binary digits" differ. For example: ...
1
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1answer
84 views

How to define a function which takes another function as input in Module

Let $f$ be a function of $n$. I would like to define a function $A$ with module which takes $f[n]$ as input. So for example: ...