Simpsons Rule: With for loops

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Eric 2015-5-10

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https://ww2.mathworks.cn/matlabcentral/answers/215973-simpsons-rule-with-for-loops

回答： Malek Arnous 2017-12-20

Hi, So I have a question where I have to use Simpsons rule to integrate (1-x^3)*sin(x) + exp(x^2/20) between -1 and 4 with 20 intervals. The function has 4 inputs, f(x), a,b (start and end points) and n intervals

I know that I can make this code simpler with the sum function but unfortunately I have to use loops for this exercise.

My code looks like this:

function integral = simpsonsrule(f,a,b,n)
h = (b-a)/n;
x = linspace(a,b,n);
x4=0;
x2=0;
for j=2:2:b
    x4 = x4 + f(x4);
end
for k=3:2:b
    x2= x2 + f(x2);
end
integral = (h/3)*(f(a)+ f(b) + 4*(x4)+ 2*(x2));
end

And I'm calling it like this:

clear;
integral = simpsonsrule((1-x.^3)*sin(x) + exp(x.^2/20),-1,4,20)

But I'm getting the error: Undefined function or variable 'x'. but haven't I defined it with x=linspace(a,b,n)?

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采纳的回答

Walter Roberson 2015-5-10

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在 MATLAB Online 中打开

integral = simpsonsrule(@(x) (1-x.^3)*sin(x) + exp(x.^2/20),-1,4,20)

You need the @(x) to make an anonymous function

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Walter Roberson 2015-5-10

What kind of n are you using?

Eric 2015-5-10

I've been using 20,50,100,500,1000.

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