trapezoidal rule with user define function

John Jessy

2020 7 2

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I am new in matlab.i want to create user define function for trapezoidal rule in which i want to take input arguments a,b,n, and the intervals values.I have seached alot but all function taking a function in argument not interval values..

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John Jessy 2020-7-3

在 MATLAB Online 中打开

I want to take interval values such as x=[0 2 4 6 8] and f(x)=[3 7 11 9 3], i dont want to use function f to calculate the trapezoidal in user define function. I want to take x and y as input in function with variable a,b and n

function r = trapezoidal(f, a, b, n)
% TRAPEZOIDAL Numerical integration from a to b
% with n intervals by the Trapezoidal rule
h = (b-a)/n;
s = 0.5*(f(a) + f(b));
for i = 1:n-1
    s = s + f(a+i*h);
end
r = h*s;

Output:

>> f = @(x)sin(x);
>> I1 = trapezoidal( f, 0, pi/2, 1 )
I1 =
   0.785398163397448

John D'Errico 2020-7-3

编辑：John D'Errico 2020-7-3

But this seems not to make any sense at all.

You want to pass in the actual vectors x and y? If so, then it makes no sense to also pass in a, b, and n. If you already have x as a vector, then x is given. If you already have y as a vector, then f as a function is irrelevant.

Are you asking how to write the trapezoidal rule for VECTORS x and y as already given?

I would note there is absolutely no reason to do this, since you already have the function trapz which does exactly that. trapz is part of MATLAB already. So unless this is your homework assignment, then there is no need.

So what would the function header look like? Start out one line at a time.

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