I'm getting an error "Undefined function 'Romberg' for input arguments of type 'char'." I'm trying to code the romberg integration method.

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peter el murr 2020-11-24

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https://ww2.mathworks.cn/matlabcentral/answers/660753-i-m-getting-an-error-undefined-function-romberg-for-input-arguments-of-type-char-i-m-trying-t

编辑： peter el murr 2020-11-28

在 MATLAB Online 中打开

I'm trying to code the romberg integration method. I think I coded it right but I'm not getting why I have thi error.

This is the function.

function[t , r] = Romberg (fun, a, b, nmax)
f = inline(fun);
r(1, 1) = (b - a) * (f(a) + f(b)) / 2;
for i = 1 : nmax
    h(i) = (b-a) /2^(i) ;
   m = 0;
    for k = 1 : (2^(i))-1
        m = m + f (a+k*h(i));
    end
    r(i + 1, 1) = (h(i) / 2) * (f(a) + f(b) + 2*m);
    for j = 2 : i
        r(i, j) = r(i, j-1) + (r(i, j-1) - r(i - 1, j - 1)) / (4^(j-1) - 1);
    end
end
t = r (i, j)

And this is it's call.

clc; clear all; close all;
a = 0;
b = pi;
nmax = 3;
fun ='sin (x)'  ;
[t, r]= Romberg (fun, a, b, nmax)

This is the error I'm getting.

Undefined function 'Romberg' for input arguments of type 'char'.

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Walter Roberson 2020-11-24

Did you store the code in Romberg.m ?

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回答（1 个）

Stephan 2020-11-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/660753-i-m-getting-an-error-undefined-function-romberg-for-input-arguments-of-type-char-i-m-trying-t#answer_554848

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For me it worked:

a = 0;
b = pi;
nmax = 3;
fun ='sin (x)'  ;
[t, r]= Romberg (fun, a, b, nmax)
function[t , r] = Romberg (fun, a, b, nmax)
f = inline(fun);
r(1, 1) = (b - a) * (f(a) + f(b)) / 2;
for i = 1 : nmax
    h(i) = (b-a) /2^(i) ;
   m = 0;
    for k = 1 : (2^(i))-1
        m = m + f (a+k*h(i));
    end
    r(i + 1, 1) = (h(i) / 2) * (f(a) + f(b) + 2*m);
    for j = 2 : i
        r(i, j) = r(i, j-1) + (r(i, j-1) - r(i - 1, j - 1)) / (4^(j-1) - 1);
    end
end
t = r (i, j)
end

gives:

t =
    1.9986
t =
    1.9986
r =
    0.0000         0         0
    1.5708    2.0944         0
    1.8961    2.0046    1.9986
    1.9742         0         0