why my iteration prog doesn't work ?

Question

khalid boureeny 2017-1-23

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/321540-why-my-iteration-prog-doesn-t-work

评论： Walter Roberson 2017-1-25

% 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
%-----------------------------------------------------------

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khalid boureeny 2017-1-25

编辑：Walter Roberson 2017-1-25

在 MATLAB Online 中打开

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 khalid_boureeny@yahoo.com

Walter Roberson 2017-1-25

在 MATLAB Online 中打开

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

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Answer 1

Walter Roberson 2017-1-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/321540-why-my-iteration-prog-doesn-t-work#answer_251712

在 MATLAB Online 中打开

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