Error in matrix dimension and using a plus sign?

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Snirisa Gödel
Snirisa Gödel 2013-6-19
I am trying to write a code for the Midpoint rule given by :
M = \sum_{i=1}^{n}hf(\frac{x_{i-1}+x_{i}}{2})
My MATLAB code is following:
if true
function M = mittpunkt(fun,a,b,n)
h = (b-a)/n;
x = linspace(a,b,n);
f = fun(x);
M = h*(sum(f(((1:n-1)+(1:n))/2)));
end
My error is :
Error using +
Matrix dimensions must agree.
If something is wrong I think it must me the index, certainly not the use of a plus sign, right? Thanks

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采纳的回答

the cyclist
the cyclist 2013-6-19
In the line where you calculate M, you are trying to add
(1:n-1)
and
(1:n)
which are vectors of two different lengths. Those are the dimensions that don't match.

更多回答（1 个）

Andrei Bobrov
Andrei Bobrov 2013-6-19
编辑：Andrei Bobrov 2013-6-19
Wikipedia about your problem:
function M = mittpunkt(fun,a,b,n)
h = (b-a)/n;
x = linspace(a,b,n);
f = fun(x);
%M = h*(sum(f(((1:n-1)+(1:n))/2))); your code
M = h*sum(f(1:end-1)+f(2:end))/2; % from Wikipedia
end

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