Error msg in fminbnd

Hi all

I an trying to find minimum value of function using fminbnd sing this script

x=linspace (0,6);
y=6*cos(x)+1.5*sin(x);
plot (y);

[xmin,fval]=fminbnd(y,2,4)

Error using fcnchk
FUN must be a function, a valid character vector expression, or an inline function object.

Error in fminbnd (line 198)
funfcn = fcnchk(funfcn,length(varargin));

But it give me an error mgs as shown, i don't understand what part in my code that have mistake.

Answer 1

[AL]

fun = @(x) 6*cos(x) + 1.5*sin(x); % Define the function

x_min = fminbnd(fun, 0, 6); % Find the minimum within the interval [0,6]

y_min = fun(x_min); % Evaluate the function at the minimum x value

plot(linspace(0,6), fun(linspace(0,6))); % Plot the function

hold on

plot(x_min, y_min, 'ro'); % Mark the minimum point on the plot

hold off

disp(['The minimum value of y is ', num2str(y_min), ' at x = ', num2str(x_min)]);

Try this Once.

[nirwana]

It works! thank...but i stil need explaination why i got the error msg in case. Is it because i define x=linspace (0,6)?

[John D'Errico]

@tyta nirwana

fminbnd solves for the minimum of a FUNCTION. When you define x as a vector, then create y, as a VECTOR, y is just a list of numbers. It is not a function anymore, so fminbnd must fail.

What @AL did was create fun as a function. And now it works.

[nirwana]

Thanks a lot @John D'Errico. Now I understand