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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

Continuing on with my current "equations and functions" obsession, I have made an Implicit Equation Grapher

It basically calculates each pixel and tries to find 0. It has trouble with missing parts of the domain, for example tan() goes from "negative large number" to "positive large number" so assumes it is 0 in between and I am not sure how to convince it otherwise (without heaps of code and very slow response).

It is nonetheless heaps of fun seeing the different things it can do.

Play with it and let me know how you go.

Post interesting equations, too.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

Fun toy! My favourite one that I've found so far is sin(5x) = cos(5x).

Why did the vector cross the road?

It wanted to be normal.

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

Cool! Thats just what I need.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi MathsisFun;

Nice grapher!

Playing with this one.

*Last edited by bobbym (2009-10-03 01:21:35)*

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**simron****Real Member**- Registered: 2006-10-07
- Posts: 237

This is really great!

I like sin(x)=tan(y).

Linux FTW

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

Haha, bobbym's is crazy.

Why did the vector cross the road?

It wanted to be normal.

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

Try this.

`y=abs(x)*tan(3*sqrt(x^2+y^2))`

Its actually an Archimedean spiral superimposed on its reflection in the *y*-axis (recall that an Archimedean spiral has the form *r* = *aθ* in polar coordinates). To fit more turns into the picture, try y=abs(x)*tan(4*sqrt(x^2+y^2)), y=abs(x)*tan(5*sqrt(x^2+y^2)), etc.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi MathsisFun;

Seems to be okay, haven't been able to crash it.

Like this one:

*Last edited by bobbym (2009-10-03 12:49:03)*

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

I am so glad everyone likes it!

Some really wild equations, too

An example of where it goes wrong is bobby's "x^2*cos(x)=y*tan(y)" ... I don't believe the horizontal straight lines should be there at +/-π/2, they are an artifact of tan(y) changing sign, so the program assumes there is a zero in there.

The program has no way of knowing that the magical zero point is undefined. Any ideas on how to solve this?

A simpler example is "1/(1+x)=y"

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Maths;

Is it the vertical asymptote you don't like for 1 / ( 1 + x ) = y ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

bobbym wrote:

Is it the vertical asymptote you don't like for 1 / ( 1 + x ) = y ?

Correct.

I have been able to "suppress" lines like that by skipping over values above, say 100, but that may also miss valid points.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi MathsisFun;

If you go here:

And enter in the top box, just as it is written below:

Plot[1/(x+1),{x,-5,5}]

You will see that yours is fine. At least for this graph.

*Last edited by bobbym (2009-10-03 17:25:03)*

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

Thanks bobby,

That gives me some courage. So perhaps Wolfram and I can simply put it down to an ill-defined domain.

I am still not happy, but I have tried different techniques and they all have side effects.

I will put some warning on the page to cover it.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

I have given it *ZOOM* capabilities.

You should see **cos(x)+sin(x*y)=cos(y*x)+sin(y)** , but that is hard on the poor program!

I also mentioned about the "extra lines" ... does it seem a reasonable explanation?

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

MathsisFun;

Graphing is always a problem. You can only sample a finite amount of points. There are equations that look different with different scales even in math packages and graphic calculators.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**simron****Real Member**- Registered: 2006-10-07
- Posts: 237

One thing I'd like to see is recognizing that xy is the same thing as x*y.

Another one I like is tan(x*y)=sin(x)+cos(y).

Linux FTW

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

simron wrote:

One thing I'd like to see is recognizing that xy is the same thing as x*y

That is a good idea, possibly hard, but I will look into it.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi all;

Working fine:

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

bobbym wrote:

Try .

*Last edited by JaneFairfax (2009-10-06 09:39:33)*

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

Whoa, that would make a good logo.

BTW, I have called it an "Implicit Equation Grapher", but maybe it should just be "Equation Grapher" ... ?

Or something else?

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Jane;

Jane wrote:

That's a nice one. It looks meaner than mine.

Hi MathsisFun;

Since it can graph explicit forms, I guess you can call it "The Grapher" or "The Plotter".

We can make a small improvement on Jane's improvement.

*Last edited by bobbym (2009-10-06 04:14:47)*

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

Or .

*Last edited by JaneFairfax (2009-10-06 09:41:57)*

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Jane;

Or this one:

I especially like the feathered effect at the corners.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,656

Love them!

I added a Print button.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi MathsisFun;

Do you think it would be possible to save the graph in some format like jpeg or gif so that the graph could be used in a post ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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