# Questions tagged [faq]

Frequently Asked Question – a tag for original questions which have a multitude of duplicates

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### How to clear up RAM without exiting kernel?

I am trying to implement the code which generates some table, works with it, extracts some numbers, add them to some other table, then clears the table (only the table and not the other elements of ...
157 views

### With vs. Block scoping of parameters for Plot

A very basic question.. Why does Block work, but not With, to specify value of a parameter for a function to be plotted? ...
146 views

### How to preserve scaled circular shapes when combining graphics?

The following code g1 = Graphics[{Thickness[0.01], Line[{{0, 0}, {10, 10}}], Disk[{5, 3}, Scaled[0.1]]}, Frame -> True] produces the following output I then ...
714 views

### Why changing to float-point value does't improve the speed?

I am testing the first tip of this article Use floating-point numbers if you can, and use them early. I've compared a pair codes and finding it's not helpful to use the float-point number during ...
188 views

### Keep only rules that replace integers with other integers

Let's say I have a list of replacement rules: List1 = {2 -> 3, b -> 5.5, 6.57 -> 2, 3 -> 4.5, 1 -> -1, 0.03 -> 0.5, 9 -> a} The desired ...
333 views

### Grid with Frame->All: How to not draw frames around empty cells?

If I have a grid of values that doesn't divide evenly, for example a list of 17 values, and split it into a 7x3 grid, then draw frames around each element: ...
21k views

### Why should I avoid the For loop in Mathematica?

Some people advise against the use of For loops in Mathematica. Why? Should I heed this advice? What is wrong with For? What ...
2k views

### Capital Letters that are built-in symbols

I'm trying to search for an answer to "What is the complete list of single capital letters that represent built-in Mathematica commands, symbols, or uses?" For example: C, D, E, I, N, O Is this ...
573 views

### Package functions and symbolic calculations

I'm writing my package (.m) in Mathematica and when I call the function it returns 0 instead of a right output. Here's my code: Package.m ...
1k views

### Piecewise Function, Explanation of Extra Case

Consider: Can someone explain why the 0, True occurs? As a second question, I like to fill the endpoints as follows: ...
31k views

### What do the X and Y axis stand for in the Fourier transform domain?

In Wolfram Mathematica the function Fourier has the following declaration Fourier[list] And after a list is given to the ...
5k views

### Changing Values in an Association using Map

I am trying to change the value of one key in an association based on the value of another key in that association. So if my association starts as: ...
3k views

### A problem about function N

Toady,I have a problem about N,described as below: For example N[1/3, 5] (* ==> 0.33333*) and ...
952 views

### Efficient method for Inserting arrays into arrays

This is strongly related to the following Questions: Looking for a way to insert multiple elements into multiple positions simultaneously in a list Building matrices by attaching vectors (columns) ...
15k views

### Matrix Multiplication in context of row and column vectors

I've been looking at some matrices in Mathematica and I've noticed something very weird: they're extremely temperamental when it comes to dot products! For example, if I have the following, ...
7k views

### Error entering equation in DSolve

I entered a command incorrectly as follows: DSolve[{y'[x]=y[x]},y[x],x] I am now experiencing: ...
654 views

### Understanding NDSolve::ndsz

I'm working on a largeish system of differential equations where I encounter the NDSolve::ndsz step size is effectively zero; singularity or stiff system suspected ...
35k views

### How can I plot implicit equations?

If you enter the following into Wolfram | Alpha, you get nice graphs: graph 4 x^4 + y^2 = 2 How do you do this in Mathmatica? I realize that these are not ...
10k views

### How to plot periodic function's graphic?

How to plot periodic function's graphic? For example, $f(t) = t$ when $-5<t<5$ and $f(t+10) = f(t)$. ...
2k views

### Mathematica not plotting whole logarithmic function

I am trying to use the following input Plot[Log[E,x+1],{x,-50,50},PlotRange->50] however the output is: How can I adjust it so the line goes down to the <...
532 views

### Preventing cell height adjustment when rotating 3D graphics

I have a large dataset of scattered x,y,z coordinates. I am trying to use ListPointPlot3D to identify outliers in 3D. This involves generating a plot and then ...
564 views

### Unexpected behavior of rule matching a pattern

I am a beginner exploring the world of Mathematica. I expected the following code T[6, 5, 4, 1, 2, 3] /. {T[a___, 1, b___] -> Length[List[b]]} should return ...
13k views

### Replace very small numbers by zero in the output of a list

I have a long nested list, but many elements are numbers of order 10^-18 or less, e.g. ...
6k views

### Extracting variables from an expression

I'm looking for a way to extract a list of variables from an expression, for example with an input like: ...
3k views

### Enforcing correct variable bindings and avoiding renamings for conflicting variables in nested scoping constructs

Using global variables the following turns an "expression" into a Function: expr = 2 x; Function[x, Evaluate[expr]] Of course ...
2k views

### Splicing a list of arguments into a function with Sequence

Not sure if this has been asked, but I have a fairly simple operation that I don't know the syntax for. Say I have an array with some values, and a function f that accepts an arbitrary number of ...
119k views

### What are the most common pitfalls awaiting new users?

As you may already know, Mathematica is a wonderful piece of software. However, it has a few characteristics that tend to confuse new (and sometimes not-so-new) users. That can be clearly seen from ...
10k views

### How to modify function argument?

Usually in programming languages, function arguments are normal local variables, which can be modified. Is this not true in Mathematica? ...
4k views

### White regions in DensityPlot?

When I try to supply my own ColorFunction Mathematica seems to partially ignore it, and the white color "burns through" if the function is too "sharp&...
17k views

### How do I work with Root objects?

I want to solve the trigonometric equation : $$(3-\cos 4x )\cdot (\sin x - \cos x ) = 2.$$ I tried Solve[(3 - Cos[4*x])*(Sin[x] - Cos[x]) == 2, x] It returns the ...
48k views

### How do I identify the source of a "Tag times protected" error?

I have some code that looks like Table[ a = 1; b = {2, 3} c = i;, {i, 2} ] which gives an error: Set::write: Tag Times in c {2,3} is Protected....
8k views

### How do I convert an argument list to a sequence of arguments?

I think this is a basic question, but I am having difficulty finding the answer in the documentation. Thread is not what I am looking for, I think. Suppose that I ...
665 views

### Confused by (apparent) inconsistent precision

$$e^{\pi \sqrt{163}} \approx 262537412640768743.99999999999925$$ E^(Pi Sqrt[163.0]) N[E^(Pi Sqrt[163.0]), 35] NumberForm[E^(Pi Sqrt[163.]), 35] returns <...
4k views

### How are parameters evaluated for a Plot in Manipulate

I am trying to get my head around how Manipulate evaluates functions in a Plot. I have read the introduction to Manipulate, and introduction to Dynamic, but I still ...
912 views

### Nested definition: How can I define a function with a passed-in expression?

Here's a simplified version of what I'm trying to do: ...
2k views

### Why are all the lines commented when I create a Mathematica script?

When I created a Mathematica script, I found that all my lines were commented out (when opened with vi or gedit or any other ...
3k 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: ...
4k views

### Function in Table

I need a table with the elements made of pure functions and list elements. This is a simplified example: I need a list as: ...
95k views

### Assign the results from a Solve to variable(s)

I understand Mathematica can't assign the results of a Solve to the unknowns because there may be more than 1 solution. How can I assign the 4 values of following result to variables? ...
4k views

### Can a function be made to accept a variable amount of inputs?

I have a function that takes two inputs and processes them for a single output. What I need is one that can take a varying number of inputs. and process them to a single output. Is this possible in ...
1k views

### Programming with Dynamic

I don't understand the following: f[a_, b_] := a + b ls = {1, 2, 3}; MapThread[f, {ls, {10, 20, 30}}] This yields ( as expected ) {11,22,33} If I change ...
798 views

### Dr. StrangeNumbers or: How I Learned to Stop Worrying and Love Floating Point Arithmetic

The following is the program. ...
991 views

### Change the height of a function being plotted

How do I alter the height of any function plot using the Plot function? Mathematica seems to limit the height of the plot up to the range of a function and distort ...
2k views

### Combining values in one column (or part) when values in another column (or part) match

Consider the following: ...
11k views

### Finding real roots of negative numbers (for example, $\sqrt{-8}$)

Say I want to quickly calculate $\sqrt{-8}$, to which the most obvious solution is $-2$. When I input $\sqrt{-8}$ or Power[-8, 3^-1], Mathematica gives the ...
10k views

### Can I simplify an expression into form which uses my own definitions?

This seems like a simple thing to do, but I couldn't find anything relevant from Mathematica documentation. So suppose I have an expression: a*b/(a + a*Cos[a/b]) ...
25k views

### How to avoid returning a Null if there is no "else" condition in an If construct

I need to use If but with only one option that is if "a" then do "b", else do nothing. So I wrote If[a,b] but the problem is ...
17k views

### Replacing composite variables by a single variable

To replace a single variable by another variable, one can simply use the the replace all (/.) operator (e.g., ...
I am trying to plot a polynomial of degree $29$ on the domain $[0,1]$, with fairly large coefficients: ...