Not sure if output is right

bobbym · 2013-12-01 06:54:29

There are other reasons for divergence. Poor initial conditions is one reason. The condition number for that matrix if I remember was around 500. That is not too bad.

evinda · 2013-12-01 07:13:56

bobbym wrote:

There are other reasons for divergence. Poor initial conditions is one reason. The condition number for that matrix if I remember was around 500. That is not too bad.

The condition number for n=500 is for example 1.2550e+005 ..
So,is it right that the methods do not converge for this matrix ??
Because,for example,both of the methods do converge for an other tridiagonal matrix,that has the number 4 at the main diagonal,1 at the first diagonal below this and also 1 at the first diagonal above this.
Which is the difference??

bobbym · 2013-12-01 07:15:15

I believe that there is a simple answer to that.

evinda · 2013-12-01 07:17:24

bobbym wrote:

I believe that there is a simple answer to that.

Could you tell me,which it is??:

bobbym · 2013-12-01 07:22:33

You have a 4 on the diagonal and 1 on the other 2 diagonals? That matrix according to some books is diagonally dominant. This makes convergence easy in the Gauss Seidel method.

But we are straying from the point of this thread. Did you try post #18's matrices? Did they converge for you? What did you notice about the new A?

evinda · 2013-12-01 08:13:31

bobbym wrote:

You have a 4 on the diagonal and 1 on the other 2 diagonals? That matrix according to some books is diagonally dominant. This makes convergence easy in the Gauss Seidel method.
I understand...
But we are straying from the point of this thread. Did you try post #18's matrices? Did they converge for you? What did you notice about the new A?

No,the matrix of post #18 does not converge,neither using the jacobi,nor the gauss-seidel method..

bobbym · 2013-12-01 08:34:40

Something is wrong with your program. That converges for me. Are you setting initial conditions to [0,0,0,0]?

Check this page to see how to increase Matlabs precision:

http://www.mathworks.com/help/symbolic/ … igits.html

See you a bit later, I need some rest.

evinda · 2013-12-01 10:24:06

bobbym wrote:

Something is wrong with your program. That converges for me. Are you setting initial conditions to [0,0,0,0]?
Check this page to see how to increase Matlabs precision:
http://www.mathworks.com/help/symbolic/ … igits.html
See you a bit later, I need some rest.

I used the command digits bit I didn't get any result!!! why??

bobbym · 2013-12-01 14:44:32

The correct comand is DIGITS:= something.

evinda · 2013-12-02 08:05:29

I get this error message:Error: The expression to the left of the equals sign is not a valid target for an
assignment.

I would like to ask you also something else..Is this right that the spectral radius of the iteration matrix of the 250x250 Hilbert Matrix,when we apply the Gauss-Seidel method is 1,and when we apply the Jacobi method 217.3320?

Last edited by evinda (2013-12-02 08:26:01)

bobbym · 2013-12-02 08:28:08

http://www.mathworks.com/help/symbolic/ igits.html

The examples on that page do not work?

evinda · 2013-12-02 08:43:45

bobbym wrote:

http://www.mathworks.com/help/symbolic/ igits.html
The examples on that page do not work?

They work...But I can't apply them at a matrix

bobbym · 2013-12-02 08:44:59

Why not? What are you entering for the matrix?

evinda · 2013-12-02 10:48:46

bobbym wrote:

Why not? What are you entering for the matrix?

I wrote this:DIGITS:=hilb(15) and I get Error: The expression to the left of the equals sign is not a valid target for an
assignment.

bobbym · 2013-12-02 15:35:47

DIGITS is a global variable. It sets the precision for everything. Try DIGITS:= 25

evinda · 2013-12-04 09:43:24

I get this message:??? DIGITS:=25
|
Error: The expression to the left of the equals sign is not a valid target for an
assignment.

But...anyway...I will let it like that...I have a last question..Could you tell me which is the iteration matrix ,for example of the hilbert matrix with a specific dimension,or for another matrix using the gauss-seidel method,and which it is using the jacobi method ,so I can check if my result is right???

bobbym · 2013-12-04 22:02:22

Hi;

Did you get convergence for the matrix in post #18?

Math Is Fun Forum

#26 2013-12-01 06:54:29

Re: Not sure if output is right

#27 2013-12-01 07:13:56

Re: Not sure if output is right

#28 2013-12-01 07:15:15

Re: Not sure if output is right

#29 2013-12-01 07:17:24

Re: Not sure if output is right

#30 2013-12-01 07:22:33

Re: Not sure if output is right

#31 2013-12-01 08:13:31

Re: Not sure if output is right

#32 2013-12-01 08:34:40

Re: Not sure if output is right

#33 2013-12-01 10:24:06

Re: Not sure if output is right

#34 2013-12-01 14:44:32

Re: Not sure if output is right

#35 2013-12-02 08:05:29

Re: Not sure if output is right

#36 2013-12-02 08:28:08

Re: Not sure if output is right

#37 2013-12-02 08:43:45

Re: Not sure if output is right

#38 2013-12-02 08:44:59

Re: Not sure if output is right

#39 2013-12-02 10:48:46

Re: Not sure if output is right

#40 2013-12-02 15:35:47

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#41 2013-12-04 09:43:24

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#42 2013-12-04 22:02:22

Re: Not sure if output is right

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