Why do my loops only run once

Question

Raquel Terrer van Gool 2020-4-14

0
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https://ww2.mathworks.cn/matlabcentral/answers/517800-why-do-my-loops-only-run-once

评论： Raquel Terrer van Gool 2020-4-14

function I=simpson13(f,a,b,n)
 
h=(b-a)/n; % length of the interval
total=0;
x=a;
fa=f; 
x=b;
fb=f;
 
for i=1:2:n-1;
   x=i*h;
   fn=f+total;
   total=fn;
end
 
for j=2:2:n-2;
   x=j*h;
   fm=f+total;
   total=fm;
end
I=(h/3)*(fa+fb+4*fn+2*fm);
end

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Raquel Terrer van Gool 2020-4-14

编辑：Geoff Hayes 2020-4-14

在 MATLAB Online 中打开

I have n=6:

x=0;
n=6; % n is the number of intervals and must be > 0 and even
a=0; b=pi;% a is the lower bound and b is the upper bound
f=5+13*sin(x); % Function
 
I=simpson13(f,a,b,n)

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Answer 1

Geoff Hayes 2020-4-14

1
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在 MATLAB Online 中打开

Raquel - the MATLAB debugger is helpful in cases like this. If you put a breakpoint in your simpson13 you would notice a problem with the input parameter f. Look closely at how it is being assigned

x=0;
n=6; % n is the number of intervals and must be > 0 and even
a=0; b=pi;% a is the lower bound and b is the upper bound
f=5+13*sin(x); % Function

f is not a function in this case but is a scalar value (5) since x is zero. If you want f to be an anonymous function then you need to assign it as

f = @(x)5+13*sin(x);

where nthe @ operator creates the handle, and the parentheses () immediately after the @ operator include the function input arguments. You will need to change how this function is used in your code as well. For example,