Error msg in fminbnd

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nirwana
nirwana on 16 Mar 2023
Commented: nirwana on 16 Mar 2023
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.

Accepted Answer

AL
AL on 16 Mar 2023
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.
  3 Comments
John D'Errico
John D'Errico on 16 Mar 2023
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
nirwana on 16 Mar 2023
Thanks a lot @John D'Errico. Now I understand

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