error in fminbnd and in my live function

i have to find the minimum Radius and Area using two equations:

V = 1/3 * pi*r^2*h and A = pi*r*sqrt(r^2 + h^2)

first i had to find area without using h, so i solved V for h, then substituted

A = pi*r*sqrt(r^2 + V/((1/3)*pi*r^2))

I then had to make a live function detailing this, using V as a global V

function A = area

global V = 10 % constant volume in in^3

r = radius; % changing radius in inches

A = pi*r*sqrt(r^2 + V/((1/3)*pi*r^2));

end

my next step was to find the minimum r and area

[rmin,Amin] = fminbnd(@area, 0.5, 5)

this got me two error messages

1. Incorrect use of '=' in the live function
2. error in fminbnd : x= xf; fx = funfcn(x, varargin{:})

How do i fix these errors?

Answer 1

[Torsten]

Don't you have to include the circular area G = pi*r^2 at the bottom ?

Then add pi*r^2 to A as indicated below.

V = 10;  % constant volume in in^3
[rmin,Amin] = fminbnd(@(r)area(r,V),0,50)

rmin = 1.8901

Amin = 19.4393

hmin = V/(1/3*pi*rmin^2)

hmin = 2.6730

function A = area(r,V)
  A = pi*r*sqrt(r^2 + (V/(1/3*pi*r^2))^2); %+ pi*r^2;
end