[Scilab-users] fsolve including linear interpolation

[paul.carrico at free.fr]

the example I built is not relevant and it does not reflect the problem
behind... sorry for the inconvenient 

Paul 

Le 2017-04-18 17:20, roger.cormier at ncf.ca a écrit : 

> Paul:
> 
> It appears that you're solving for y given theta and x, but y is a
> linear function of theta and x.
> 
> I don't have a good knowledge of what you are trying to solve, but
> when I solve nonlinear problems I normally either have a form of
> first-order derivative (scalar or a Jacobian), or some form of
> branching/discontinuity from which I need to choose the "best"
> solution. For linear interpolation, I find that it's easier to simply
> write a function myself than try to figure out how to make a given
> built-in function works.
> 
> I'm going fishing here: in your function, theta is 8x1 but your
> arguments for interpl are theta(:,1),theta(:,2), which presumes that
> theta is 8x2, so that could be a place to start looking at why fsolve
> is giving your grief.
> 
> Regards,
> 
> Roger.
> 
> ______________________________________________
> Dr. Roger Cormier, P.Eng.
> Home Tel. & Fax: 613-823-7299
> 
> Am mar. 18 avr. 2017 um 09:03 schrieb paul.carrico at free.fr:
> 
>> Hi All
>> 
>> I'm wondering what is the way to solve the following study (but at the same time I'm not sure that the problem has been correctly posed) ... I'm a bit "disrupted" by theta scalar that depends itself on x value.
>> 
>> The problem seems to be non linear and I tried (but I failed) in using fsolve.
>> 
>> Any suggestion where I've to see to?
>> 
>> Thanks for your time and help
>> 
>> Paul
>> 
>> #################################################
>> function y=calculus(x)
>> 
>> theta = [ 1 100 200 300
>> 
>> 1000 1200 1500 2000]';
>> 
>> theta_interp = interp1(theta(:,1),theta(:,2),x,'linear');
>> 
>> y = -theta_interp * 0.268 + 120 -x; //pause
>> 
>> // if theta = 1 : y = 0 -> x = 120 - 0.268 = 119.73
>> 
>> // if theta = 100 : y = 0 -> x = 120 - 26.8 = 93.2
>> 
>> // if theta = 200 : x = 66.4
>> 
>> // if theta = 300 : x = 120 - 0.268 = 39.6
>> 
>> // can we say that y belongs to [39.6 , 119.73] ?
>> 
>> endfunction
>> 
>> [x,v,info] = fsolve(0,calculus)
>> 
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