Unrecognized function or variable 'X0'.

when i run the command it says "Unrecognized function or variable 'X0'." I need help. Thank you

[X, FVAL]= FSOLVE(@mintafun,X0,options),

[Dyuman Joshi]

You need to define x0 and options outside of the ODE function.

And the function is fsolve in lower case. Also, there are multiple typos in your code (bracket misplaced, multiplication or division sign missing, etc) check out for them.

[Bismark]

i don't understand the first sentence please kindly clarify. x0 =[10, 4 6 , etc] in the code. I will go over the code to check the last statement. thank you.

[Stephen23]

"x0 =[10, 4 6 , etc] in the code"

x0 is not the same as X0

[Bismark]

i don't understand what that means

Answer 1

[Cris LaPierre]

There are actually a lot of errors with your code. It might be worth taking a step back and thinking through your approach.

First, MATLAB is case-sensitive, which means FSOLVE and fsolve, X and x, etc are not equivalent statements.

Second, you have created a function that appears to be written upside down. It also appears to contain at the very bottom the inputs you are using to call the function in fsolve.

Third, you must be explicit in your use of mathematical operators to use. MATLAB does not assume anything. For example, sigma(X(14) should probably be sigma*(X(14)

Finally, check for typos. For example ((X13) should probably be (X(13)

As for the error you are seeing right now, it is likely because you are trying to call your function without defining the inputs. Here, for example, I haven't defined the variable X0 yet.

[X, FVAL]= FSOLVE(@mintafun,X0,options),

Unrecognized function or variable 'X0'.

The correct syntax might look like this, at which point, you will start getting new errors due to the other issues I describe above.

x0 = [10; 6; 4; 3; 4; 3; 2; 3; 18; 7; 25; 10; 5; 5; 4; 11; 8; 20; 6; 3; 8; 1; 30; 7; 2; 6; 14; 30;]; 
options=optimset('Display','iter'); 
[X, FVAL]= fsolve(@mintafun,x0,options),

[Cris LaPierre]

Here's a simple example adapted from the fsolve documentation page.

x0 = [0,0];
x = fsolve(@root2d,x0)

Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.

x = 1×2

0.3532 0.6061

function F = root2d(x)
y = 0.5;
F(1) = exp(-exp(-(x(1)+x(2)))) - x(2)*(1+x(1)^2);
F(2) = x(1)*cos(x(2)) + x(2)*sin(x(1)) - y;
end

[Bismark]

"Second, you have created a function that appears to be written upside down. It also appears to contain at the very bottom the inputs you are using to call the function in fsolve." kindly explain this for me.

Are you implying i start with X(1), X(2) ....etc. Should the equations be in ascending order of X?

[Cris LaPierre]

I refering to your defining equations that use variables that have not yet been defined. You can't use a variable (or array element, if that is your intent) if it hasn't yet been created.

Here's a shortened example

x0 = [10; 6; 4; 3; 4; 3; 2; 3; 18; 7; 25; 10; 5; 5; 4; 11; 8; 20; 6; 3; 8; 1; 30; 7; 2; 6; 14; 30];
F1 = mintafun(x0)

Unrecognized function or variable 'phi'.

Error in solution>mintafun (line 6)
F =X(5)/X(12) - phi*(1 - tau_c)*X(1) / theta*(1 - tau_w)*(1-X(4));

% The very first calculation uses phi, tau_c, theta, and tau_w, none of which exist yet.
function F = mintafun(X)
F =X(5)/X(12) - phi*(1 - tau_c)*X(1) / theta*(1 - tau_w)*(1-X(4));
tau_c = 0.17;
tau_w = 0.2;
theta = 0.349;
phi = 5;
end

[Bismark]

Perfect.Thank you