Help with code: Matlab code not printing last verification line.

Question

Tyw7 2015-10-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/248157-help-with-code-matlab-code-not-printing-last-verification-line

评论： Geoff Hayes 2015-10-12

I can't get Matlab to print the last "data within tolerance" line:

function [integral] = intmidpoint(N)
clear
clc
%INTMIDPOINT numerical integration using the composite midpoint rule
    clc
%define the integration limits
    a=0;
    b=2;
    %this is the aim of absolute error required
aim = 0.001;
%define the number of sub-intervals to be used
    if nargin == 1
        n=N;
    else
        n=1;
    end
    h=(b-a)/n;
%approximate integral using the composite mid-point rule
      integral=0.0;
%add the contribution of each sub-interval in turn
abs_err = realmax;
while abs_err>aim;
        h=(b-a)/n;
    integral=0.0;
     for i=1:n;
        x_left = a+(i-1)*h;
        x_right = a+i*h;
        x_half = (x_left+x_right)/2.0;
        f_half = f(x_half);
        integral = integral+h*f_half;
        abs_err=abs(4-integral);
       end;
       fprintf('2 Midpoint approximation to integral using %g subintervals is %g.  \n Data outside of tolerance.  Abosolute error is %g, which is greater than 0.001. Increase the number of steps.  \n',n,integral,abs_err);
       n = n + 1; 
      if abs_err>aim;
          continue;
     fprintf('test Midpoint approximation to integral using %g subintervals is %g.  \n Data within tolerance.  Absolute error is %g, which is less than 0.001. \n',n,integral,abs_err);        
      end;
end;
end
%subfunction defines the integrand
function [f_value] = f(x)
    f_value = (x)^3;
end

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Answer 1

Walter Roberson 2015-10-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/248157-help-with-code-matlab-code-not-printing-last-verification-line#answer_195651

The "continue" is going to be executed before the fprintf() that is in the same "if"

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Walter Roberson 2015-10-12

You want break rather than continue

Geoff Hayes 2015-10-12

在 MATLAB Online 中打开

Try this

 if abs_err>aim
     fprintf('test Midpoint approximation to integral using %g subintervals is %g.  \n Data within tolerance.  Absolute error is %g, which is less than 0.001. \n',n,integral,abs_err); 
     break;       
 end

Note that the

 ans =
      3.9990

is the output parameter returned from your function call. You are probably calling your function from the command line without assigning the output to a variable. Try calling your function as

[estIntegral] = intmidpoint(42);

to suppress the extra output. (Note that it is the use of the semi-colon that is suppressing the output.)

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