fsolve question ('undefined function or variable')

Hi, i'm trying to solve this code:

function g=llamada

x0=[0.1 0.03]

[dfinal]=fsolve(@(d) febrerodosmilcatorce2(q,d),x0)

function f=febrerodosmilcatorce2(q,d)

L1=10;

D=0.02;

L2=1.5;

L3=0.3;

C1=10;

C2=4000;

G=9.81;

L=0.03;

A=8/(pi^2*G*D^4);

AD=8/(pi^2*G*d^4);

f=[-L*L1*A*q^2/D+C1-C2*q^2-L*L2*A*q^2/(9*D)-L*L3*A*q^2/(9*D)-A*q^2;-L*L1*A*q^2/D+C1-C2*q^2-4*L*L3*AD*q^2/(9*d)-L*L2*AD*q^2/(9*d)-4*L*L3*AD*q^2/(9*d)-A*q^2];

I want that the first function calls the second one giving it two inputs (q and d) and that one returns me the final value of d.¿Can anyone help me?

Thanks

Answer 1

[Alan Weiss]

It could be that the reason you want to run this complicated syntax is that you have not understood that MATLAB optimization functions optimize a single variable, usually called x. So if you want to solve for two variables, q and d, you can put them into a single vector x along the following lines:

 function F = theObjective(x)
 q = x(1);
 d = x(2);
 L1=10;
 D=0.02;
 L2=1.5;
 L3=0.3;
 C1=10;
 C2=4000;
 G=9.81;
 L=0.03;
 A=8/(pi^2*G*D^4);
 AD=8/(pi^2*G*d^4);
 F = [-L*L1*A*q^2/D+C1-C2*q^2-L*L2*A*q^2/(9*D)-L*L3*A*q^2/(9*D)-A*q^2;...
   -L*L1*A*q^2/D+C1-C2*q^2-4*L*L3*AD*q^2/(9*d)-L*L2*AD*q^2/(9*d)-4*L*L3*AD*q^2/(9*d)-A*q^2];

Call the solver like this:

 x0 = [0.1 0.03]
 x = fsolve(@theObjective,x0)

Good luck,

Alan Weiss

MATLAB mathematical toolbox documentation

[alvaro laguna]

Thank you Alan, i didn't Know that 'limitation' in the Matlab syntax.

Regards.

Answer 2

[Geoff Hayes]

alvaro - what is the full error message? fsolve is part of the Optimization Toolbox, so you will need it in order to have access to this function. If you don't have this toolbox, then you are most likely seeing the

 Undefined function 'fsolve' for input arguments of type 'function_handle'.

error.

From the command line, type ver to see which toolboxes you have installed. If you have this toolbox then type

 which fsolve -all

to see if you may have a conflicting function.

[alvaro laguna]

Hi Geoff first of all thanks for your response. I have already the 7.1 version of the Optimitation toolbox. I think that it could be the way i call the second function because if I write both like this:

function g=llamada

x0=[0.1 0.03]

[dfinal]=fsolve(@(q) febrerodosmilcatorce2(q),x0)

function f=febrerodosmilcatorce2(q)

L1=10; D=0.02;

L2=1.5;

L3=0.3;

C1=10;

C2=4000;

G=9.81;

L=0.03;

A=8/(pi^2*G*D^4);

AD=8/(pi^2*G*q(2)^4);

f=[-L*L1*A*q(1)^2/D+C1-C2*q(1)^2-L*L2*A*q(1)^2/(9*D)-L*L3*A*q(1)^2/(9*D)-A*q(1)^2;-L*L1*A*q(1)^2/D+C1-C2*q(1)^2-4*L*L3*AD*q(1)^2/(9*q(2))-L*L2*AD*q(1)^2/(9*q(2))-4*L*L3*AD*q(1)^2/(9*q(2))-A*q(1)^2];

I get what i think that is the correct answer (q(1)=0.0011 and q(2)=0.0233) the problem is that i want only that the second function returns me the second value (q(2)) which i namered before as d.

Regards