what's wrong here? plz help

hl=0.0;                  % Assigning lower value xl
hu=2.0;                        % Assigning upper value xu
R=3;
err=2;
v(1)=10;
i=1;
while err>0.01;
hr = (hl+hu)/2;                % Calculating root value xr
Vhr=(pi*((hr)^2)*(3*R-hr))/3;
err=abs(Vhr-30);
      if  err < 0.1        % Breaking while loop when condition is met
              break;                        
      end
Vhl= (pi*((hl)^2)*(3*R-hl))/3;        % Calculating f(x) with lower value xl
      if Vhl*Vhr < 0        % Check the condition
              hu=hr ;        % Replacing upper value with root value xr
      else
              hl=hr ;        % Replacing lower value with root value xr
      end
end
display (hr)

[Maria Esmeral]

Your values never change, are fixed values (hl, hu...)so your err is always bigger than 0.01. Create vector with your parameters so they can vary with a loop or something like that.

Answer 1

[Azzi Abdelmalek]

That means that err is always bigger than 0.01.

Answer 2

[Maria Esmeral]

 hl=[0:0.1:100];                  % Assigning lower value xl
hu=[0:0.1:100];                        % Assigning upper value xu
R=3;
err=2;
v(1)=10;
i=1;
while err>0.01;
  for i=1:length(hl) 
    for j=1:length(hu)  
        hr = (hl(i)+hu(j))/2;                % Calculating root value xr
        Vhr=(pi*((hr)^2)*(3*R-hr))/3;
        err=abs(Vhr-30);
        Vhl= (pi*((hl(i))^2)*(3*R-hl(i)))/3;        % Calculating f(x) with lower value xl
              if Vhl*Vhr < 0        % Check the condition
                      hu(j)=hr ;        % Replacing upper value with root value xr
              else
                      hl(i)=hr ;        % Replacing lower value with root value xr
              end
        if  err < 0.1     
            break
        end    
    end
      if  err < 0.1     
        break
      end 
  end
  if  err < 0.1        % Breaking while loop when condition is met
    break                        
  end  
end
display (hr)

Maybe not the best but it works.

Answer 3

[Roger Stafford]

The trouble is that your initial values for hl and hu both give the same sign, namely positive, to your function to begin with. For your algorithm to work, it is necessary for the upper and lower function signs to always be opposite. Therefore change to something like hl = 1; and hu = 12; initially, which makes the initial signs opposite.