error in large integers

I am currently working with fractions involving 10digit integers.

for example, typing 1168347147/863334886 into MATLAB produces the answer 4045/2989.

But I want to store the fractions exactly. How do I go about doing this?

Many thanks.

Answer 1

[Aldin]

Hi,

use vpa functon

for example:

vpa('4045/2989',100) ---> for hundred digits

[Walter Roberson]

No, you cannot get "fractions exactly" by using VPA. Try vpa('1/3') for example: the representation you get will not be of 1/3 because 1/3 is an infinitely repeating decimal.

[Aldin]

I have one even better solution:

>>1168347147/863334886

ans =

1.3533

USE "rats" function:

>>rats(ans)

the result will be: 4045/2989

[Eigo Takkeda]

I wish to use the value 1168347147/863334886 and store it exactly for further calculations, but MATLAB automatically rounds it to 4045/2989, and therefore looking for a way to avoid this rounding.

[Aldin]

I think is more better to use smaller number like 4045/2989 ???

[Aldin]

Do you know:

1168347147/863334886 = 4045/2989

Answer 2

[Walter Roberson]

If you have the symbolic math toolbox, then

sym('1168347147/863334886')

Note that the result will be a symbolic number, not a double precision number.

[Eigo Takkeda]

could I then use this for further calculations?

[Walter Roberson]

Yes, if you do have the symbolic toolbox then you would be able to use symbolic numbers in further calculations; the results would be symbolic numbers.

There might be places along the way where you needed to convert the symbolic numbers to double precision using double(), as there are MATLAB routines that cannot work with symbolic numbers.

[Aldin]

Hello sir Walter,

Can you please explain:

>> sym('1168347147/863334886')

ans =

1168347147/863334886

>> ans * 1,4

ans =

8178430029/4316674430

--------------------------

But if i check last result with 'vpa' function i got this:

>> vpa('863334886*1,4)

ans = 1208668840.4