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1. Open calculator.

2. Enter a square number like 25.

3. Click on the square root button in the calculator.

4. Now subtract the result from the square root of the number, in this case 5.

5. Click '=' button on the calculator and note that the result is not 0.

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

Hi;

It is not a bug.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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Is it a different way of expressing Zero?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

First congratulations, half a zillion programmers will never know that in their entire life! A zillion math types do not believe it! They suspect that big bad Mi**8cr---o$--oft is at it again. For once they are not to blame.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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If it not a bug, whats it?

I didn't understand what you're talking of

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,015

Isn't this the precision stuff you always mention, bobbym?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

Isn't this the precision stuff you always mention, bobbym?

Computer math ≠ human math

Okay, first you must get the spiel.

The hardest thing for computers to do is arithmetic. People find that amazing but it is true. The problem is not a bug but it is inherent in the way computers do arithmetic.

1) To a computer the number line is not solid like they draw it in mathematics. Instead it looks like the dots and dashes of morse code. This is because some numbers do not exist for a computer. For instance there is no 1 / 3 on its number line, just a big hole.

2) (a - b)(a+b)≠(a^2 - b^2). Algebraically equal expressions are not equal to a computer.

3) Addition is not commutative.

The order of addition can drastically affect the answer!

4) A computer can not subtract or multiply without possible disastrous error.

5) You never use the quadratic formula to solve a quadratic equation because on a computer it will give inaccurate results.

6) Newton's iteration though taught is rarely the best one for the job.

7) A computer can not compare theoretically equal quantities.

and many more.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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So, Is it possible that human beings will eventually develop something better?

5) You never use the quadratic formula to solve a quadratic equation because on a computer it will give inaccurate results.

Would you give an example?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

Hi Agnishom;

Yes, we could come up with something better. A human brain! But I think that has already been made.

Here is a whole bunch of examples that I worked on for MIF:

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,015

I remember the problem on calculating sqrt(3.0000000000000001)-sqrt(3) you posed. Everything gives out 0 when the expression is evaluated directly, even M!

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

Yes, without taking special pains on that one, subtractive cancellation will wipe out the answer.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,523

Agnishom wrote:

1. Open calculator.

2. Enter a square number like 25.

3. Click on the square root button in the calculator.

4. Now subtract the result from the square root of the number, in this case 5.

5. Click '=' button on the calculator and note that the result is not 0.

they have a bug

The integral of hope is reality.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

One way or another all math programs will do this, even Mathematica.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

**Online**

**mathgogocart****Member**- Registered: 2012-04-29
- Posts: 1,523

bobbym wrote:

One way or another all math programs will do this, even Mathematica.

Thats Funny.

The integral of hope is reality.

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And sad....

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 103,735

Hi Agnishom;

It is a property of how computers and mathematics mix. Once you know about it you are prepared. We will go over it when the the time comes.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**philandy****Member**- Registered: 2013-06-10
- Posts: 11

If you had to use binary, decimal, and floats all at the same time, you might come up with sqrt(4)-2=-8.1648465955514287168521180122928e-39 as well. Notice the sqrt(1)-1 is fine. Personally I prefer to use the Google Dual-Mode Calculator app in Google mode, which gives sqrt(4)-2=0.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,548

hi

It's not a bug. It is just that calculators and computers can only do arithmetic imperfectly. Numbers are represented at machine code level by binary numbers. All fractions that do not have a power of two as the denominator have a recurring binary form. Since no machine can hold an infinite number of binary digits, it is inevitable that the representation will involve some sort of truncation of the true value. This leads to tiny errors between the value calculated and the true answer.

In the early days of calculators it was much more common to find such errors arising. Two things (at least two; there must be more that I don't know about) can improve the situation. (i) Increase the number of binary digits used to represent the number; (ii) use guard digits. The latter means that more digits are used than are displayed. The guard digits are used to round off the displayed results. This eliminates a lot of the problem.

On a calculator you can reveal the guard digits by doing a sum and then subtracting the displayed answer from itself. The difference is the guard. If rounding up has occurred you need to adjust what you see displayed by one to allow for the rounding.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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