[Scilab-users] Solving linear simultaneous equations

[aweeks at hidglobal.com]

Hi Paul,

I have a suggestion but also a more general observation.

I have also been solving simultaneous linear equations of the form A * x =
b.  My first thought was to use the method:

	x = A \ b

and it seemed to me that if Tunji's equations are well-behaved then this
may be the easiest method, rather than using 'linsolve'.

In my case I'm trying to solve electrical circuit equations which are
sparse and include complex values.  I used  x = A \ b to begin with but for
some component values I get messages like:

	Warning :
	matrix is close to singular or badly scaled. rcond =    1.0388D-08
	computing least squares solution. (see lsq).

The method goes to completion but the results are obviously wrong.
If I use 'linsolve' instead, it goes to completion without producing any
warnings or errors but the results are wrong.
For me, 'umfpack' is the best method by far and works very well.

This is a situation which has occurred several times before.  SciLab is a
very powerful piece of software and as a result there may (apparently) be
several methods of doing the same thing but there are rarely explanations
of how each method works or why you would use one method rather than
another.

Best wishes,

Adrian.

                                          
 Adrian Weeks                             
 Development Engineer                     
                                          
                                          
 HID Global,                              
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 Green Meadow Springs                     
 Business Park,                           
 Cardiff CF15 7AB,                        
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 (Office)                                 
 aweeks at hidglobal.com                     
 www.hidglobal.com                        
                                          





                                                                                                                                  
  From:       Paul Bignier <paul.bignier at scilab-enterprises.com>                                                                  
                                                                                                                                  
  To:         "International users mailing list for Scilab." <users at lists.scilab.org>, iootunniyi at futa.edu.ng                     
                                                                                                                                  
  Date:       18/03/2014 10:01                                                                                                    
                                                                                                                                  
  Subject:    Re: [Scilab-users] Solving linear simultaneous equations                                                            
                                                                                                                                  
  Sent by:    "users" <users-bounces at lists.scilab.org>                                                                            
                                                                                                                                  






Hi Tunji,

linsolve help page contains utilization examples.

If you still cannot use it, please tell us more about the problem you are
trying to solve.

Regards,
Paul


On 03/18/2014 10:16 AM, 'Tunji OTUNNIYI wrote:
      Hello:

      I am quite a starter here.

      Could someone please help me through solving n x n linear
      simultaneous equations.
      I saw linsolve in help, but can’t follow through the arguments.
      Applying the calling sequence to a simple example will be of help.
      Thanks a lot.

      Tunji OTUNNIYI | MME SEET FUTA Akure, Nigeria.





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