lsqnonlin with vector input and multiple equations.

when I try to run my model I always receive the error 'Undefined function or variable 'x'.'

How should I specify my variable x?

function y=testst(T_1,T_2,P_c,Q_gen)

x_1=0.35

x_2=0.21

y_3=0.85

h_1=1500

h_2=500

h_3=230

f(1)=x(1)-x(2)-x(3);

f(2)=x_1*x(1)-x_2*x(2)-y_3*x(3);

f(3)=Q_gen+x(1)*h_1-x(2)*h_2-x(3)*h_3;

steadystate=@(x) f(x);

st=[0.005 ;0.005; 0.005]';

lb=[0; 0 ;0];

ub=[1 ;1 ;1];

x=lsqnonlin('steadystate',st,lb,ub)

y=x

end

I also tried this:

st=[0.005 ;0.005;0.005];

lb=[0; 0 ;0];

ub=[1 ;1;1];

y=lsqnonlin(@(x) steadystate(x,x_1,y_3,h_1,h_2,h_3,Q_gen),st,lb,ub);

function f= steadystate(x,x_1,x_2,y_3,h_1,h_2,h_3,Q_gen)

f(1)=x(1)-x(2)-x(3);

f(2)=x_1*x(1)-x_2*x(2)-y_3*x(3);

f(3)=Q_gen+x(1)*h_1-x(2)*h_2-x(3)*h_3;

end

but than I had 'not enough input arguments'

Answer 1

[Pravin Jagtap]

Hello Emma,

The error mentioned is caused because of the way 'function handle' is used (steadystate=@(x) f(x);). In your case, it is better to write the separate function which returns 'f(1)', 'f(2)' and f(3) values. Please refer to the following example for creating the function handle:

function f = get_f(x)
    f(1) = x(1);
    f(2) = x(2);
    f(3) = x(3);
end

Then, run the following script to see how to create the function handle:

f = @get_f;
x = [1 2 3];
steadystate = f(x)

Here, ‘steadystate’ will be 1x3 vector. Modify your code using above reference and for more details on how to use function handles use the following documentation link:

https://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html