error : Function integration trapezoidal

Question

jakv 2013-12-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/108504-error-function-integration-trapezoidal

评论： Sam 2023-4-14

i want to calculate area from numerical integration of function f(x) with the limits a to b and vary n . by the way i use this code from my handbook, numerical chapra. to solve my problem. but the result was error.

function I = trap(func,a,b,n,varargin)
% trap: composite trapezoidal rule quadrature
%   I = trap(func,a,b,n,p1,p2,...):
%                  composite trapezoidal rule
% input:
%   func = name of function to be integrated
%   a, b = integration limits
%   n = number of segments (default = 100)
%   p1,p2,... = additional parameters used by func
% output:
%   I = integral estimate
if nargin<3,error('at least 3 input arguments required'),end
if ~(b>a),error('upper bound must be greater than lower'),end
if nargin<4|isempty(n),n=100;end
x = a; h = (b - a)/n;
s=func(a,varargin{:});
for i = 1 : n-1
  x = x + h;
  s = s + 2*func(x,varargin{:});
end
s = s + func(b,varargin{:});
I = (b - a) * s/(2*n);

the error :

??? function I = trap(func,a,b,n,varargin)
    |
Error: Function definitions are not permitted in this context.

what should i do ?

--- my purpose is to make the table like below this text, to known how the error result with vary n parameter.

%

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sixwwwwww 2013-12-3

you can't directly run this function. first save it in an m-file with name 'trap.m' and then call with appropriate input parameters from command prompt or from another script

jakv 2013-12-3

what the script that i can use ? sorry i'm newbie.

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Answer 1

sixwwwwww 2013-12-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/108504-error-function-integration-trapezoidal#answer_117163

Maybe following links are helpful for you for this purpose:

http://www.youtube.com/watch?v=qo3AtBoyBdM

http://www.youtube.com/watch?v=AzvOc5odmDg

These links shows how to use matlab functions. and how to input and get output values from them

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Ahzabuddin 2016-5-20

can you help me too??? I get trapezoidal single... but I have trouble unequal trapezoidal.

x = [0 .12 .22 .32 .36 .4 .44 .54 .64 .7 .8];

y = 0.2+25*x-200*x.^2+675*x.^3-900*x.^4+400*x.^5;

>>trapuneq(x,y)

??? Undefined function or variable 'l'.

Error in ==> trapuneq at 18

s = s+(x(k+l)-x(k))*(y(k)+y(k+l))/2;

my formula M-File is

if nargin<2,error('at least 2 input arguments required'),end

if any(diff(x)<0),error('x not monotonically ascending'),end

n = length(x);

if length(y)~=n,error('x and y must be same length'); end

s = 0;

for k = 1:n-1

s = s+(x(k+l)-x(k))*(y(k)+y(k+l))/2;

end

I = s;

Sam 2023-4-14

Changing the 2 "l"s ("L"s; Capital shown for variable clarity) to a "1" ("One") in the line of the For loop fixes the error and allows the same anser to be attained as shown in the textbook (1.5948).

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