why my iteration prog doesn't work ?

% Use NR method f(x)= x^3-5x^2+7x-3 
clc
TV=3;
x=(4);
tol=0.0007;
format long
for i=1:5;
    fx=(x(i))^3-5*(x(i))^2+7*(x(i))-3;
    fxx=3*(x(i))^2-10*(x(i))+7;
    x(i+1)=(x(i))-(fx/fxx);
    E_T(i)=(abs((TV-x(i+1))/TV))*100;
end
for i=1:5;
    e(i)=(x(6))-(x(i));
    fx=(x(i))^3-5*(x(i))^2+7*(x(i))-3;
    fxx=3*(x(i))^2-10*(x(i))+7;
    fxxx=6*(x(i))-10;
    e(i+1)=(-fxxx/2*fxx)*(e(i))^2;
end
if abs(TV-(x(i+1)))<tol
    disp(' enough to here')
    disp(' -----------')
    disp('  x(i+1) ')
    disp(' -----------')
    x;
     disp(' -----------')
     disp('   T.V   ')
     disp(' -----------')
     E_T;
     disp(' -----------')
     disp('   E(i+1)   ')
     disp(' -----------')
     e;
     disp(' ------------- ')
end
%-----------------------------------------------------------

[John D'Errico]

Sure it works. It does exactly what it does. Of course, we don't know what you want it to do, since you don't tell us.

If we could actually read it, we might be more willing to help you. So why not learn to format your code as code?

Edit the question. Select the block of text that is code, then click on the "{} Code" button above the edit window. Your code will now be readable as code.

Then tell us what the code does wrong. Do you get an error? Does it just return the wrong thing? What do you expect it to do?

If you want help from people, then why not make it possible for people to give you help?

[KSSV]

What is that not working here?

[khalid boureeny]

Hi,John D'Errico .... when I start the program, I don't get any results .... I expect something like

 x(i+1)=3.0000000557

and T.V=0.00000007424 and E(i+1)=-0.000000089144 ... otherwise , i got a message about E_T .... Thanks for helping me , I'm new with matlab but I really need in my faculty ...

[khalid boureeny]

Hi, John D'Errico ... I always got this message : The variable ' E_T' appears to change size every loop iteration (within a script) . Consider preallocating for speed. ....thanks again.

[Walter Roberson]

That is an efficiency warning; it is telling you that your code could possibly be made faster. It is not an error message. You could get rid of it by starting out with

E_T = zeros(1,5);

[khalid boureeny]

Hi , Walter Roberson .... I'm deeply grateful for your help ... I still have a problem with decimal digits ...

What if I need more decimal digits in my answer than the default ? for example 50 or 80 digits .

PLEASE , HELP in this one ...

clear all
clc
x=(-0.1);
 y=(0);
 fprintf(' i        x          \n')
fprintf(' ---  ------------- \n')

     for i=1:5;
       fx=(x(i))^3-(x(i))^2+2;
       fxx=3*(x(i))^2-2*(x(i));
       y(i)=x(i)-(fx/fxx);
       fy=(y(i))^3-(y(i))^2+2;
       fyy=3*(y(i))^2-2*(y(i));
       x(i+1)=x(i)+([fy-fx]/fyy);
     end
   for i=1:length(x)
       fprintf('%2i %18.15f\n',i,x(i))
   end

   THE RESULTS ARE
   i        x          
   ---  ------------- 
   1 -0.100000000000000
   2 -3.119140528362807
   3 -1.474069695697443
   4 -1.017351956185236
   5 -1.000001047082565
   6 -1.000000000000000

MY e-mail is [e-mail]

[Walter Roberson]

If you need 50 or 80 digits you will need to switch to the Symbolic Toolbox, and display using vpa()

NumDig = 50;
x = sym(-0.1);
y = sym(0);
fprintf(' i        x          \n')
fprintf(' ---  ------------- \n')

     for i=1:5;
       fx=(x(i))^3-(x(i))^2+2;
       fxx=3*(x(i))^2-2*(x(i));
       y(i)=x(i)-(fx/fxx);
       fy=(y(i))^3-(y(i))^2+2;
       fyy=3*(y(i))^2-2*(y(i));
       x(i+1)=x(i)+([fy-fx]/fyy);
     end
   for i=1:length(x)
       fprintf('%2i %s\n', i, char(vpa(x(i),NumDig)))
   end

Answer 1

[Walter Roberson]

In your section

if abs(TV-(x(i+1)))<tol
    disp(' enough to here')
    disp(' -----------')
    disp('  x(i+1) ')
    disp(' -----------')
    x;
     disp(' -----------')
     disp('   T.V   ')
     disp(' -----------')
     E_T;
     disp(' -----------')
     disp('   E(i+1)   ')
     disp(' -----------')
     e;
     disp(' ------------- ')
end

remove the ';' from the 'x;' and 'E_T;' and 'e;' -- so

if abs(TV-(x(i+1)))<tol
    disp(' enough to here')
    disp(' -----------')
    disp('  x(i+1) ')
    disp(' -----------')
    x
     disp(' -----------')
     disp('   T.V   ')
     disp(' -----------')
     E_T
     disp(' -----------')
     disp('   E(i+1)   ')
     disp(' -----------')
     e
     disp(' ------------- ')
end

[khalid boureeny]

Hi, Walter Roberson .... thanks a lot , I will try ... thanks again ...

[khalid boureeny]

Hi , Walter Roberson .... YOU're a genius ... thanks again ...thanks thanks .

Answer 2

[Lateef Adewale Kareem]

increase your number of iteration, you will meet the tolerance target

[khalid boureeny]

Thanks , I will try ...