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Re: 2 linear eq
From: |
shih lin |
Subject: |
Re: 2 linear eq |
Date: |
Mon, 7 Feb 2005 21:31:37 -0800 |
thanks your help, but in a matlab 7 bood (mastering matlab7, by Duane
Hanselman,
Bruce Littlefield, by Prentice Hall) page 165, there is a line:
/************************************************************/
>> mat2str(pi*eye(2)) % convert to matlab input syntax form!
/***************************************************************/
it look for me the constant coefficent can put before the variable by * as
multiplicstion even it is linear in matlab,
/*I tried last time's quadratic eq, put a 8 * before both x(1), x(2) , it can
run. in 2.1.42 */
regard eric
>Date: Tue, 8 Feb 2005 13:44:29 -0500
> Geordie McBain <address@hidden> shih lin <address@hidden>Cc: address@hidden
> Re: 2 linear eq
>On Mon, Feb 07, 2005 at 07:27:49PM -0800, shih lin wrote:
>> to solve 8x + y =-29
>> 8x - y = -19
>>
>> I do
>>
>> >> function z=f(x)
>> z=[8*x(1)+x(2)=-29, 8*x(1)-x(2)=-19];
>> endfunction
>> >> fsolve("f",[0,0])
>> error: invalid lvalue function called in expression
>> error: evaluating assignment expression near line 2, column 17
>> error: evaluating assignment expression near line 2, column 4
>> error: called from `f'
>> error: fsolve: evaluation of user-supplied function failed
>> >>
>> I am in GNU Octave, version 2.1.42 (i686-pc-cygwin), if anyone can point how
to
>> upgrade I am highly appreciate(I get it just follow download website's
>> instruction)
>>
>> eric
>
>No, the function passed to fsolve shouldn't contain the equations, it
>should return the residuals. Here you'd need
>
> function z = f(x)
> z = [8,1;8,-1]*x + [29;19];
> endfunction
>
>This works O.K.:
>
> octave> fsolve ("f", [0;0])
> ans =
>
> -3.0000
> -5.0000
>
>However, since your equations are linear, you don't really need fsolve
>(it's only required for nonlinear equations). You can solve linear
>systems like yours by:
>
>octave> [8,1;8,-1] \ [-29;-19]
>ans =
>
> -3
> -5
>
>Geordie McBain
>www.aeromech.usyd.edu.au/~mcbain
>
>
>On Mon, Feb 07, 2005 at 07:27:49PM -0800, shih lin wrote:
>> to solve 8x + y =-29
>> 8x - y = -19
>>
>> I do
>>
>> >> function z=f(x)
>> z=[8*x(1)+x(2)=-29, 8*x(1)-x(2)=-19];
>> endfunction
>> >> fsolve("f",[0,0])
>> error: invalid lvalue function called in expression
>> error: evaluating assignment expression near line 2, column 17
>> error: evaluating assignment expression near line 2, column 4
>> error: called from `f'
>> error: fsolve: evaluation of user-supplied function failed
>> >>
>> I am in GNU Octave, version 2.1.42 (i686-pc-cygwin), if anyone can point how
to
>> upgrade I am highly appreciate(I get it just follow download website's
>> instruction)
>>
>> eric
>
>No, the function passed to fsolve shouldn't contain the equations, it
>should return the residuals. Here you'd need
>
> function z = f(x)
> z = [8,1;8,-1]*x + [29;19];
> endfunction
>
>This works O.K.:
>
> octave> fsolve ("f", [0;0])
> ans =
>
> -3.0000
> -5.0000
>
>However, since your equations are linear, you don't really need fsolve
>(it's only required for nonlinear equations). You can solve linear
>systems like yours by:
>
>octave> [8,1;8,-1] \ [-29;-19]
>ans =
>
> -3
> -5
>
>Geordie McBain
>www.aeromech.usyd.edu.au/~mcbain
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- 2 linear eq, shih lin, 2005/02/07
- Re: 2 linear eq, miguel manese, 2005/02/07
- Re: 2 linear eq, Mike Miller, 2005/02/07
- Re: 2 linear eq, miguel manese, 2005/02/08
- Re: 2 linear eq, Paul Thomas, 2005/02/08
- Re: 2 linear eq, Henry F. Mollet, 2005/02/08
- Re: 2 linear eq, Paul Laub, 2005/02/08
- Re: 2 linear eq, John W. Eaton, 2005/02/08
- Re: 2 linear eq, Przemek Klosowski, 2005/02/08
Re: 2 linear eq, Geordie McBain, 2005/02/08
- Re: 2 linear eq,
shih lin <=