Questions about the use of built-in Mathematica functions, including pure functions.

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3
votes
1answer
2k views

Nested If statements

When I do this: Apply[(If[#2 == what, "yay", If[#2 == whoops, "nay"]]) &, {-5, what}] I get: yay But when I do this: ...
3
votes
2answers
291 views

Handling Indeterminate Forms

I'm running a sum, the elements of which are calculated by calling functions that I wrote. The only issue is, I've implemented this pretty stupid solution where I have 4 or 5 (nested!) if statements ...
4
votes
1answer
247 views

How to organize and run functions?

I am very new to Mathematica. I thought I would try it out for my first assignment in my computer science class. Until now I have only used C-base languages including C#, Java, Objective-C, and ...
8
votes
1answer
301 views

ReplaceAll[] and Limit[] don't give correct results for this expression under extreme variables [duplicate]

Possible Duplicate: Funny behaviour when plotting a polynomial of high degree and large coefficients 1/x^2 + (3 + x)/(6 (1 - Exp[x] + x)) ——This is a ...
1
vote
1answer
165 views

Computing a logarithmic function

Possibly this is a very lame question for this site. There is a function $f(n)=-\ln(a*n); \space \Bbb Z \to \Bbb R$, and I want to define $a$ for pairs of values. For example: $f_1(n_1)=15; ...
4
votes
4answers
556 views

How to define and use a linear function

I have the following equation $T = -800n + 12000$. I know that this is a linear function and that the two points $(0, 12000)$ and $(15,0)$ lie on the line. When I have 2 other values of n between 0 ...
1
vote
2answers
337 views

Piecewise function with a function as argument

I want to define a piecewise function, which has two arguments, one of which is a function of the other's piecewise argument. I am giving an example ...
1
vote
2answers
134 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
3answers
726 views

Variables Inside Functions Not Evaluating

x = 5*y function1[y_] := x function1[5] Am I wrong in thinking that function1[5] should equal 25? Instead this comes out. ...
1
vote
1answer
151 views

Using an InputField to define a function to compose with a sequence

I am still trying to figure out Mathematica (started early August). I am trying to write a program that will accept an arbitrary function and an arbitrary sequence that can start at an arbitrary ...
5
votes
3answers
244 views

First evaluation fails

I am fairly new to Mathematica (version 7), so please bear with me... I have duplicated, in Mathematica, a program that I originally wrote in C (it generates OEIS sequence A191837). The problem is ...
16
votes
8answers
547 views

Applying And to lists of Booleans

I'd like to take {True,True,False} and {True,False,False} and apply And to get ...
13
votes
7answers
367 views

Get the first element after the first sequence of length N of consecutively increasing values

I'm looking for an efficient way of extracting the first element after the first sequence of N consecutive elements in which the values are increasing. If these are the data of a toy example: ...
8
votes
2answers
657 views

Determine whether some expression contains a given symbol

Given a symbol t and an expression expr, how can I determine whether or not the symbol t ...
1
vote
1answer
114 views

How to explain the results of the following integrals?

Why does the following program lead to different results of a21 and a211? ...
2
votes
3answers
346 views

How can `SquareWave` be used as the input in `OutputResponse`?

I'd like to compute the response of a TransferFunctionModel when driven by a SquareWave. Here's a simple example, ...
13
votes
6answers
2k views

Counting negative values in list

I would like to count the negative values of a list. My approach was Count[data, -_] which doesn't work. How can I tell Mathematica to count all numbers with ...
4
votes
2answers
290 views

Implementation of builtin function Fold

In the documentation for fold, it says Fold[f,x,list] gives the last element of FoldList[f,x,list]. But this is surely not the way it is implemented, right? ...
7
votes
1answer
279 views

RootSum result manipulation/simplification

Consider the sum sum1 = Sum[ k/( k^7 - 2 k + 3), {k, Infinity}] ...
3
votes
1answer
193 views

Evaluation of self-defined functions

I defined a function that I call disc which I want to minimize later. The function is defined as ...
-1
votes
1answer
249 views

Why is the CTRL + / not working?

I've learned how to use this shortcut to input fractions in the 2D form, it worked nice on my notebook but I can't make it on my desktop. Any tip on what could be happening?
11
votes
4answers
442 views

Assessing argument type in set delayed function definitions

I'm wondering how to properly assess the type of arguments passed to functions defined with :=. I want my functions to be the most efficient, unambiguous and clear ...
-5
votes
3answers
394 views

Constructing lists by applying functions to another list

Suppose f is a function of two variables: $f = f(x,y)\quad$ and $L$ is a list. Could someone help me in defining a list of the form: $D = \{f(x,y)\ |\ x \in L,\ y \in L\}$ I tried this: ...
16
votes
2answers
809 views

Sum or Product with Exclusions

Is there a built-in feature for handling things like: $$\sum_{i=0}_{i\ne j}^n\frac{a-a_i}{a_i-a_j}$$ and $$\prod_{i=0}_{i\ne j}^n\frac{a-a_i}{a_i-a_j}$$ or should I work out some sort of ...
1
vote
1answer
288 views

How to substitute variables in interpolated function?

I'm looking for the way to substitute variables in interpolated function again to original one. (I want to know how to get P(r, theta) from Psol(v, w).) The original variables : ...
0
votes
0answers
206 views

How Can I Use Conditional with Rational Domain Restrictions [duplicate]

I am reasking this question in a new thread. My previous post How Can I Use Solve/Reduce Output? seemed to have led to a an interesting dissussion of how to (better) solve the problem that produced ...
5
votes
1answer
902 views

How Can I use Solve/Reduce Output

Suppose I want x and y to be rationals Solve[ x^2 + y^2 == 1, {x, y}, Rationals] I am ...
3
votes
2answers
202 views

How does RootOfUnityQ work?

How does Mathematica's RootOfUnityQ function work? That is, how does Mathematica know if a number is a root of unity? Example: Let $x = \frac{1-i \sqrt{2+\sqrt{5}}}{1+i \sqrt{2+\sqrt{5}}}$. Then ...
7
votes
3answers
228 views

Get unevaluated option value?

This is kind of a follow-up to this question. I want to be able to define a function that takes an option, and then, inside the function, retrieve and test the unevaluated value of the option. For ...
3
votes
0answers
103 views

ProbabilityDistribution PDF on boundary points

I would like to evaluate the PDF of a custom ProbabilityDistribution at the min and max values. However, PDF[...] returns 0 at ...
9
votes
2answers
1k views

Pass function or formula as function parameter

I can write either Integrate[x^2, {x,0,3}] or f[x_] = x^2 Integrate[f[x],{x,0,3}] and get the same computation. Suppose I ...
8
votes
2answers
684 views

Speed up Mathematica code involving Convolve

I'm trying to plot the averaged autocorrelation function of a random wire profile $\xi(x)$ which is build from unitsteps which are each L units long. To calculate the average I'm generating nMax ...
10
votes
1answer
819 views

What is the difference between Set and SetDelayed?

I have a problem with defining a function and most of time I get confused by Set or = and ...
5
votes
2answers
483 views

Evaluating an If condition to yield True/False

I would like to decide whether an option passed to my custom function has the value Automatic or something else. This is my attempt: ...
2
votes
1answer
949 views

Function output from DSolve

I want to get a function as output form DSolve. For Example : sol = DSolve[{Q''[t] + 40 Q'[t] + 625 Q[t] == 100*Cos[10*t], Q[0] == 0, Q'[0] == 0}, Q[t], t] I ...
18
votes
1answer
287 views

What does “EquationalLogic`FindCounterexample[]” do?

I found the undocumented EquationalLogic`FindCounterexample[] by browsing the lists of available symbols, but I have no clue about its purpose. The name is ...
7
votes
2answers
1k views

Finding all partitions of a set

I'm looking for straightforward way to find all the partitions of a set. IntegerPartitions seems to provide a useful start. But then things get a bit complicated. ...
13
votes
6answers
365 views

Comparing the last output of a nested function with all the previous ones

my main question is how I can compare the last output of a nested function with all the previous ones and stop iterating when I find a repeating value. (I have 2 other questions but I think they are ...
4
votes
3answers
2k views

Why won't Mathematica Integrate my function?

My code: ...
1
vote
2answers
191 views

Expectation over a list with nested-mapped expressions

I need expected values of a list where the random variable to take expectations over should be an input into expressions defined earlier. I suspect Set[] and SetDelayed[] tripped me. (Or Map and ...
3
votes
2answers
432 views

How can I assign a Fit result to a function?

I have this code ...
2
votes
3answers
227 views

How to Compute Aggregate Best and Worst Cases for a Large Number of Estimates?

I need to aggregate multiple estimations, but I haven't been able to find a built-in function in Mathematica that aggregates multiple probablity estimations (I am specially interested in estimations ...
14
votes
5answers
5k views

How to find the domain and range of a function with Mathematica?

I'm studying calculus and in some exercises I am asked to find the domain and range of a function. Does Mathematica have already a built-in function for this? I can imagine some ways of doing so, ...
0
votes
2answers
124 views

About minimizing calculations when using ComposeList

I have a lot of functions to use in a iterative way, and I need some of the calculation results. For example: ...
6
votes
5answers
252 views

How to nest my own “times” function to get powers

I have a "times" function. I'd like to create a power function using it. It should look like this for an 6th power: ...
3
votes
2answers
314 views

What is the command to find function invariant?

What is the command to find function invariant? http://demonstrations.wolfram.com/AFunctionInvariantUnderAGroupOfTransformations/ what is algorithm it use to calculate this? Edit there is a book ...
2
votes
2answers
144 views

Custom function not returning any output

I'm trying to write a custom function but it isn't returning any output. Here's my code so far: ...
7
votes
2answers
1k views

How to create a rectangle wave (duty cycle $\ne$ 50 %)?

I'm trying to use phase-shifted SquareWave[] functions to create a rectangle wave: ...
2
votes
2answers
402 views

decompose a number (less than 255) in a sum of powers of 2

Is there a built in function that would take a number and decompose it into a sum of powers of 2? The numbers will be non negative less than 256. For what it's worth I'm trying to understand a paper ...
5
votes
1answer
125 views

How to make the Show function work in this case?

I can't get this to work, the Show function shows only the first plot. Why this happens and how to solve it? Show[Plot[x^2, {x, 2, 10}], Plot[1 - x, {x, 1, -10}]] ...