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### Check result-condition number

Posted: **Sat Nov 23, 2013 10:05 pm UTC**

by **evinda**

Hi!!

Could you tell me what is equal to the condition number of the matrix R,using the infinity norm, if R is a 50x50 tridiagonal matrix with the number 5 at the main diagonal and the number 6 at the first diagonal below this,and also the number 6 at the first diagonal above the main diagonal??

I found this result: 93.6551

Is this right??

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 5:11 am UTC**

by **NathanielJ**

Yes. More specifically, it's 4885477064818389638136352610039211133217/52164587258011922567975512864675399397.

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 10:13 am UTC**

by **evinda**

Why is my result so different from yours????

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 10:31 am UTC**

by **Flumble**

evinda wrote:Why is my result so different from yours????

Did you not notice the little / in the middle?

The only difference is that you got ~5 digits of accuracy and Nathan got the exact result.

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 10:44 am UTC**

by **evinda**

Flumble wrote:evinda wrote:Why is my result so different from yours????

Did you not notice the little / in the middle?

The only difference is that you got ~5 digits of accuracy and Nathan got the exact result.

Oh sorry!!!!!!!I haven't noticed it before.

I have also an other question.Could you tell me which is the condition number,using the infinity norm,of the Hilbert matrix with n=400..

I found it: 3.1873e+021.I found it,by writing a code in matlab.When I run it I get the following warning:Matrix is close to singular or badly scaled.Results may be inaccurate.RCOND:3.137467e-022.

Ehat does this mean???Is my result wrong???

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 6:54 pm UTC**

by **Cleverbeans**

evinda wrote:Ehat does this mean???Is my result wrong???

It means computers are not magic boxes that always give you an answer. They have limits and just like people when you give them larger problems they're more likely to make a mistake, and it is warning you about them.

### Re: Check result-condition number

Posted: **Sun Nov 24, 2013 6:56 pm UTC**

by **evinda**

Cleverbeans wrote:evinda wrote:Ehat does this mean???Is my result wrong???

It means computers are not magic boxes that always give you an answer. They have limits and just like people when you give them larger problems they're more likely to make a mistake, and it is warning you about them.

I understand..Thank you for your help