Extract a function from a table

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Sarah CHOUCHENE 2019-11-17

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https://ww2.mathworks.cn/matlabcentral/answers/491533-extract-a-function-from-a-table

评论： Sarah CHOUCHENE 2019-11-20

Hello,

I really need to clear up my toughts, I want to extract a fonction from a table of two dimensions ( l,t) that I recover from and ODE method.

[t,l]=ode23('odef',[t0,tf],l0)

My goal is to integrate "l" Si I need to have a function to use for exemple the simpson method :

f = inline('l','t')
h = 100/N;
Isim=0.0;
for i=1:N
    Isim= Isim+h*(1/6*f(t(i))+2/3*f((t(i)+t(i+1))/2)+1/6*f(t(i+1)));
end
Isim 

Of corse this program doesn't work because I used a vecto as a function !

Do you have an idea how can I integrate from data ?

Thank you,

Regards,

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Sarah CHOUCHENE 2019-11-20

在 MATLAB Online 中打开

And the diff.m is :

%DIFF Difference and approximate derivative.
%   DIFF(X), for a vector X, is [X(2)-X(1)  X(3)-X(2) ... X(n)-X(n-1)].
%   DIFF(X), for a matrix X, is the matrix of row differences,
%      [X(2:n,:) - X(1:n-1,:)].
%   DIFF(X), for an N-D array X, is the difference along the first
%      non-singleton dimension of X.
%   DIFF(X,N) is the N-th order difference along the first non-singleton 
%      dimension (denote it by DIM). If N >= size(X,DIM), DIFF takes 
%      successive differences along the next non-singleton dimension.
%   DIFF(X,N,DIM) is the Nth difference function along dimension DIM. 
%      If N >= size(X,DIM), DIFF returns an empty array.
%
%   Examples:
%      h = .001; x = 0:h:pi;
%      diff(sin(x.^2))/h is an approximation to 2*cos(x.^2).*x
%      diff((1:10).^2) is 3:2:19
%
%      If X = [3 7 5
%              0 9 2]
%      then diff(X,1,1) is [-3 2 -3], diff(X,1,2) is [4 -2
%                                                     9 -7],
%      diff(X,2,2) is the 2nd order difference along the dimension 2, and
%      diff(X,3,2) is the empty matrix.
%
%   See also GRADIENT, SUM, PROD.
%   Copyright 1984-2005 The MathWorks, Inc.
%   Built-in function.