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Jun 5th, 2007

Square root program without sqrt or pwr

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is there any way one could do a square root program without sqrt or pwr functions?

Any tips?

I am not asking for code btw.

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Is it possible to create a square root program without math.h in C++

tformed

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Jun 5th, 2007

Re: Square root program without sqrt or pwr

>is there any way one could do a square root program without sqrt or pwr functions?
No, those functions are magic. There's no way you can simulate their behavior in C++ without pixie dust or phoenix feathers. One might assume that if you know how the mathematics work, you could come up with a sensible facsimile, but in reality, only compiler writers are capable of creating such things...

Narue

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Jun 6th, 2007

Re: Square root program without sqrt or pwr

You could use a binary search algorithm. (It would be easy to name better ways, but Meh.)

Rashakil Fol

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Jun 6th, 2007

Re: Square root program without sqrt or pwr

There seems to be a rash of "do x without using the obvious" problems at the moment.

Are they all at the same school with some dim-wit teacher who thinks that learning dumb tricks is the way to teach programmers.

Salem

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Jun 6th, 2007

Re: Square root program without sqrt or pwr

lol, point me out to these threads if you can, just in case i can point them out lol

anyways, the teacher wants us to write a program without relying on these special functions. I can do them with, but now he wants us to do without.

I do not know of any mathematical formula that will enable me to achieve this without using a square root.
I will ask him, to clarify. Will post back later.

Click to Expand / Collapse Quote originally posted by Salem ...

There seems to be a rash of "do x without using the obvious" problems at the moment.

Are they all at the same school with some dim-wit teacher who thinks that learning dumb tricks is the way to teach programmers.

tformed

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Re: Square root program without sqrt or pwr

>anyways, the teacher wants us to write a program without relying on these special functions.
Yea, we figured as much. The thing is, there's no point to it if the functions are available. That's why they're there, so you don't have to write them. Anyway, a simple pow is easy to write: Just multiply x with itself y times and you have $x^y$ . sqrt is harder, but you can find examples and explanations all over the web. Most likely you don't care about efficiency for a class, so just pick the first one you find that works. Two relatively simple ones are binary search (like Rashakil suggested) and newton iteration.

Narue

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Re: Square root program without sqrt or pwr

heres one (I do not know what it is called. My friend and I were having a competition who could make the fastest sqrt algorithm, so this is mine):

c++ Syntax (Toggle Plain Text)
double sqrt(double num)
{
    double mod=1;
    double c=0;
 
    for(int d=0; d<50; c+=mod, d++)
    if(c*c>num)
    {
        c-=mod;
        mod/=10;
    }
 
    return c;
}
double sqrt(double num)
{
    double mod=1;
    double c=0;

    for(int d=0; d<50; c+=mod, d++)
    if(c*c>num)
    {
        c-=mod;
        mod/=10;
    }
    
    return c;
}

Sturm

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Jun 6th, 2007

Re: Square root program without sqrt or pwr

Obviously, my coloured in hint wasn't enough

Compare log(10000) with log(100)
Try it with a few others as well where one is the square root of the other.

Salem

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Jun 6th, 2007

Re: Square root program without sqrt or pwr

Different methods of finding the square root.

> Try it with a few others as well where one is the square root of the other.
Yes, logarithmic method seems to be a good choice.

Last edited by ~s.o.s~; Jun 6th, 2007 at 1:58 pm.

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Jun 7th, 2007

Re: Square root program without sqrt or pwr

I keep on getting the following as an error:

'ln' undefined; assuming extern returning int

do i need to define ln? If so, what value?

tformed

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