## MaplePrimes Posts

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It would be nice if the site could remember the login information, so that we don't have to log in every time.

## Mapping angles to a range of 0 to 360 degrees

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In some applications it is necessary to map an angle to a range of 0 to 360 degrees. Adding 360 degrees to an angle, or subtracting 360 from an angle does not change actually change the angle. One way to do this would be to add (or subtract) enough multiples of 360 degrees until the angle falls between 0 and 360. For example, given an angle of 400 you would subtract 360 to get an angle of 40 degrees. In Maple, this is easily accomplished by the following function.

Frem := (x,y) -> x - y*floor(x/y);

## MaplePrimes??!??

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Yesterday, I was in a Maplesoft management meeting where we concluded that the launch of MaplePrimes was to become the number one (or maybe two) priority for the company. So here it is ...

## Solitons: A Closer Look at Solitary Waves

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Solitary waves, or solitons were first described by Scott Russell, who noted the phenomenon while riding alongside a canal in 1834. He described a peculiar wave in the canal wave a single well-organized heap that propagated, seemingly without dissipation, for several miles. As a naval designer, Scott recognized that there were important things to be learned from these unusual waves.

## MaplePrimes Community Guidelines

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The rules for using MaplePrimes are simple: Respect each other and behave. Use common sense and your time on MaplePrimes will be fun and productive.

1. MaplePrimes does not allow obscene, racist, homophobic, or sexually explicit language. We reserve the right to remove postings that defame or insult anyone, as well as posts that are abusive or hateful. Any harassing posts or postings that might be construed as stalking will be deleted and made available to the proper law-enforcement officials. We also reserve the right to move or remove posts that are off the subject or not in the appropriate language.

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You understand that all messages appearing here are the sole responsibility of those persons posting the message. This means that you, and not Waterloo Maple Inc., are entirely responsible for all information and material that you post on MaplePrimes. Waterloo Maple Inc. does not control the content of any messages posted on MaplePrimes and does not guarantee the accuracy, integrity or quality of anything on MaplePrimes or any products or services that may appear here. You understand that by using MaplePrimes, you may be exposed to content that is offensive, indecent or objectionable. Under no circumstances will Waterloo Maple Inc. be liable for any errors or omissions in any postings or for any loss or damages of any kind incurred as a result of the use of any information contained in MaplePrimes.

## Why doesn't Maple recognize the standard mathematical...

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Here is an example to illustrate the problem.
```
> y := SQRT(4);
y := SQRT(4)
```
To get the square root function, you must use the name "sqrt", because Maple is case sensitive. Other examples of this are:
• use "Pi" rather than "pi" to get 3.141etc
• use "exp(1)" rather than "e" to get 2.718etc
• use "I" rather than "i" to get the square root of minus 1
Also note that, for example, "Int" and "int" are both Maple commands, but work differently.

## What does "unexpected" mean?

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Here are some examples to illustrate syntax errors.
``` > fsolve((1-x)/x^2),x);
`)` unexpected
```
In this case, I made a typing error; there is an extra right parenthesis after the "2". Removing it fixes the problem.
```
> fsolve((1-x)/x^2,x);
1.

> y : = sqrt(4);
`=` unexpected
```
In this case, the problem is that the ":=" has a blank separating the ":" and the "=".
```
> y := sqrt(4);
y := 2

> by:=3;
`:=` unexpected
```
In this case, the problem is that the variable name "by" is a word

## What does "a constant is invalid as a variable"...

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Here are some examples illustrating this problem
```
> x:=3;
...various other calculations, during which you forget that you
gave x a value
> solve(2*x=1,x);
Error, (in solve) invalid arguments

> plot(2*x,x=-1..1);  No complaint is written out, but the plot is
just the line y=6.
```
Here x already equals 3, so it doesn't make sense to use it in an assertion like "2*x=1", and plotting "2*x" is just plotting "6". Just as the above section shows an example of having too many indeterminates, this example shows what happens when there are too

## Why doesn't my function definition work?

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Here are two correct ways to define functions.
```
> f:=2-x;           One way is by assigning a formula to a name.
> plot(f,x=-1..1);  If you use this method you can refer to f,
> solve(f=0,x);     BUT referring to "f(x)" yields nonsense.
> f(x);      WRONG
2 - x(x)

> f:=x->x^2;          Another way is by using an arrow.
> f(x);               If you use this method you can refer to f(x),
> f(1);               BUT referring to just "f" only yields "f",
> plot(f(x),x=-1..1); not the function.
> solve(f(x)=0,x);
```

## When I enter the same command repeatedly, why...

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Some commands change the internal state of the calculation, so the results have to be different each time. For example, if x is 1, entering x:=x+1; repeatedly obviously yields values of x that count up. A less obvious way that a command can do different things different times it is used is if it includes the % reference to the previous result. Then, the result from the command will depend on what the previous result was. It is less confusing to assign a name to a result you want to use again, rather than referring to it with %.

## How do I undefine a variable to put it back to...

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To undefine x, enter x:='x'; To restart Maple with its memory cleared, enter restart.

## Basic Maple Commands

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Help with using the simple Maple Commands

## Help with Plotting

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Any questions that apply to plotting in Maple will appear here.

## Why did my graph turn out empty or blank?

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A1: You forgot to specify a range on the independent variable.

``` > f:=2-x;
> plot(f);              WRONG
Plotting error, empty plot
> plot(f,x=-1..1);      RIGHT
```

A2: You might be plotting a quantity that isn't defined. For example, you might have defined Y but then asked Maple to plot y. Maple is case-sensitive, and many strange behaviors are the result of typing a variable name in the wrong case.

Another way a plotted quantity can be undefined is if you didn't use the assignment operator := to define it.

``` > y=sin(x);              WRONG
```
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