Why deosnt this work?

Question

Michael Lee 2017-3-20

0
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https://ww2.mathworks.cn/matlabcentral/answers/330871-why-deosnt-this-work

评论： Michael Lee 2017-3-20

Im trying to use simpsons rule to evaluate an integral, but odd numbers dont work for simpsons. So im testing whether the number is even or not before calculating the integral. Whats the problem here?

%Matlab script to evaluate the integral of sin^3(x) between 0 and pi/2
%Prompts the user for input number of strips
prompt = 'Please enter number of strips: ';
n = input(prompt);
if mod(n,2) == 0
   %Declaration of constant and vectors
  finish = pi/2;
  h = finish/n;
  points = 0:h:finish;  % From 0 to 'finish' with steps of 'h'
  esno = 0;
  osno = 0;
%Carry out the operator element wise, for each element
v = sin(points).^3;
% Loop for finding sum of even terms
for j = 2:2:n
    esno = esno + v(j);
end
% Loop for finding sum of odd terms
for k = 3:2:n-1
    osno = osno + v(k);
end
simpval = (h/3)*(v(1) + 4*esno + 2*osno + v(n+1))
%Graphing the convergence of integral with no. of sample points
total_samples=n;
integral_value=zeros(1,total_samples);
for n_samples=1:total_samples
  X=linspace(0,pi/2,n_samples+1);
  Y=sin(X).^3;
  integral_value(n_samples)=trapz(X,Y);
end
plot(1:total_samples,integral_value)
else
      exit(0);

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Adam 2017-3-20

So what is the problem? Error? Incorrect result? No result?

Michael Lee 2017-3-20

Sorry should have said that at first. Just says continue entering statement.

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Answer 1

Steven Lord 2017-3-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/330871-why-deosnt-this-work#answer_259540

You haven't ended the if / else / end statement you started with if mod(n,2) == 0. If you put this code in the Editor, select all the code, right click, and select Smart Indent in the context menu you'll see that the if on line 5 lines up with the else on line 32, but there's no corresponding end.

FYI you probably don't want to call exit on line 33; that would quit MATLAB altogether.