positive index error in matlab

Question

shobi swaminathan 2014-1-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/113668-positive-index-error-in-matlab

评论： shobi swaminathan 2014-1-26

采纳的回答： Amit

在 MATLAB Online 中打开

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

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Answer 1

Amit 2014-1-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/113668-positive-index-error-in-matlab#answer_122145

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.

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Amit 2014-1-25

在 MATLAB Online 中打开

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