positive index error in matlab

clc;

clear all;

 R=3;
beta=8;
x1=1:1:10;

for x=1:length(x1)

    x=round(x);

f(x)=1-(exp(-((2^(R))-1)/x)^(beta/2));

df(x)=(beta/2)*(((2^R)-1)^beta)*(x^(-(beta+1)))*(exp(-((2^(R))-1)/x)^(beta/2));

    format compact
   disp('  iterate       x            f(x)          est. error  ')
   for n =  0:5

      s =( f(x)/df(x));
       sprintf('   %2d    %2.10f    %2.10f    % 2.10f \n', n,x,f(x),s)
       x = x-s;

   end
end

error is:

Attempted to access f(-62718.3); index must be a positive integer or logical.

Error in newton (line 15)

      s =( f(x)/df(x));

plzz suggest a solution

Answer 1

[Amit]

In MATLAB f(x) usage is to (if f is a matrix) access the xth element in the matrix. And Here thats why you're getting this error.

[Amit]

If I was you, I'd do something like this:

 R=3;
beta=8;
x1=1:1:10;
x = 1; % Intial value of x
for n=1:length(x1)
    f=1-(exp(-((2^(R))-1)/x)^(beta/2));
    df=(beta/2)*(((2^R)-1)^beta)*(x^(-(beta+1)))*(exp(-((2^(R))-1)/x)^(beta/2));

    format compact
    disp('  iterate       x            f(x)          est. error  ')
    % for n =  0:5

      s =( f/df);
       disp(sprintf('   %2d    %2.10f    %2.10f    % 2.10f \n', n,x,f,s));
       x = x-s;
   %end
end

[shobi swaminathan]

Thanks alot..dis code is working