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allemensen


Newbie


Joined: 21 Jul 2009
Posts: 20

Posted: 08 Apr 2010 12:13:11 pm    Post subject:

I created a symbolic program for calculating the derivative of an equation.

I'd like to know what you think about it, and possibly new features or bugs.
I think the most common operators are supported, with the exception of the "x-th power root of y"

If you have any questions about its structure, ask away!
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thornahawk
μολών λαβέ


Active Member


Joined: 27 Mar 2005
Posts: 569

Posted: 09 Apr 2010 06:53:04 am    Post subject:

I'm still reviewing your code (that's a rather long and recursive beastie you have there Smile ), though I'm wondering what you meant by not handling the power/root operators correctly; just treat x^y as e^(y*ln(x)) (with the implicit question of whether your routine can handle this composition).

Still, this looks good, thanks for posting.

thornahawk

P.S. You might want to add support for the hyperbolic functions at some point...
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allemensen


Newbie


Joined: 21 Jul 2009
Posts: 20

Posted: 09 Apr 2010 07:20:41 am    Post subject:

x^y is handled correctly, but I haven't implemented the root version (x-root y, equal to y^(1/x))

How do you differentiate hyperbolic functions (and what are they?). I've never come across them.

The previous version does have some bugs, and only accepts whole numbers, not fractions. I fixed those.
The program basically has three parts:
- string parsing, turning it into a list with operations and tokens
- differentiating the function into another list
- displaying the list

Do you have any suggestions how to speed up the code?

EDIT: found the hyperbolic functions. Their derivates are equal to cos and sin, so if you don't use both at the same time you should be fine. I might add them, as soon as I feel like doing so.
Where can they be found in the calculator, besides the catalog?


Last edited by Guest on 09 Apr 2010 08:00:27 am; edited 1 time in total
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bwang


Member


Joined: 15 Mar 2009
Posts: 128

Posted: 15 Apr 2010 09:54:05 pm    Post subject:

Hyperbolic functions don't differentiate into cos and sin; they differentiate into cosh and sinh.
They are only available in the catalog.

I don't have access to an 83/84 right now, so I can't test this. How fast is it?

What method does it use to parse expressions? Does it use a stack?
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allemensen


Newbie


Joined: 21 Jul 2009
Posts: 20

Posted: 16 Apr 2010 01:27:51 am    Post subject:

That's what I meant. cosh and sinh differentiate similarly as cos and sin. The only difference is the 'h', if you'd write it down.

It is really slow. For a complex function it will take over 10 seconds.

It parses expressions by running over a substring of the input. It evaluates the lowest priority operator and then parses the two/one/zero parts left.
It uses a stack (a list) to keep track of information such as where to split.
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