accessing single function from an array of functions

Question

Barbara Margolius 2022-3-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1663734-accessing-single-function-from-an-array-of-functions

评论： Barbara Margolius 2022-3-4

采纳的回答： Torsten

I have defined a matrix of functions:

a=@(t) (1+0.8*sin(2*pi*t));

b=@(t) .8*(1-0.8*sin(2*pi*t));

z = @(t) 0*t;

%T = matlabFunction(fmat);

T=@(t) [-3*a(t) a(t) a(t) a(t) z(t) z(t);...

a(t) -5*a(t) a(t) a(t) a(t) a(t); ...

a(t) a(t) -5*a(t) a(t) a(t) a(t); ...

b(t) b(t) b(t) -5*b(t) b(t) b(t); ...

b(t) b(t) b(t) b(t) -5*b(t) b(t); ...

a(t) a(t) a(t) b(t) 5*b(t) -3*a(t)-6*b(t)];

If I want to access just a single function from the matrix, how do I do it? I have tried several approaches and keep getting: Error: Invalid array indexing.

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Walter Roberson 2022-3-4

See https://www.mathworks.com/matlabcentral/answers/539642-is-it-possible-to-have-an-array-of-function-handles#comment_2020739

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Answer 1

Torsten 2022-3-4

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1663734-accessing-single-function-from-an-array-of-functions#answer_909949

编辑：Torsten 2022-3-4

在 MATLAB Online 中打开

f = {@(t) t, @(t) exp(t), @exp} % the second and third are equivalent
SecondFunction = f{2};
ValueOfSecondFunction = SecondFunction(1)

Does that help ?

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Barbara Margolius 2022-3-4

a = @(t)(1+0.8*sin(2*pi*t));

b = @(t)0.8*(1-0.8*sin(2*pi*t));

z = @(t)0*t;

n = 10;

%T = matlabFunction(fmat);

% T is a function of t which returns a 6-by-6 matrix.

% Each element of T is derived from the outputs of functions a, b, and z,

% which are also functions of t.

T = @(t)[ ...

-3*a(t) a(t) a(t) a(t) z(t) z(t);...

a(t) -5*a(t) a(t) a(t) a(t) a(t); ...

a(t) a(t) -5*a(t) a(t) a(t) a(t); ...

b(t) b(t) b(t) -5*b(t) b(t) b(t); ...

b(t) b(t) b(t) b(t) -5*b(t) b(t); ...

a(t) a(t) a(t) b(t) 5*b(t) -3*a(t)-6*b(t); ...

];

mysize = max(size(T(0)));

myLT = @(s)eye(mysize);

C=diag([1 2 3 -4 -3 0]);

deltat = 1/n;

mysize = max(size(T(0)));

myLT = @(s)eye(mysize);

C=diag([1 2 3 -4 -3 0]);

for k=0:n-1

tobeexp = T(k*deltat)*deltat;

myLT = @(s) myLT(s)*expm(tobeexp-s*C);

end

myLT = @(s)det(eye(mysize)-myLT(s));

myLT(.4)

28.0296

h=0:.01:.99;

plot(myLT(h));

Error using *

Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix

matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

Torsten 2022-3-4

编辑：Torsten 2022-3-4

在 MATLAB Online 中打开

h=0:.01:.99;
myLTh = arrayfun(myLT,h);
plot(h,myLTh)

But to be honest: I can't decipher what you are doing in your code.

Barbara Margolius 2022-3-4

thanks!

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Answer 2

Voss 2022-3-4

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1663734-accessing-single-function-from-an-array-of-functions#answer_909959

在 MATLAB Online 中打开

a = @(t)(1+0.8*sin(2*pi*t));
b = @(t)0.8*(1-0.8*sin(2*pi*t));
z = @(t)0*t;
%T = matlabFunction(fmat);
% T is a function of t which returns a 6-by-6 matrix.
% Each element of T is derived from the outputs of functions a, b, and z,
% which are also functions of t.
T = @(t)[ ...
    -3*a(t)    a(t)    a(t)    a(t)    z(t)           z(t);...
       a(t) -5*a(t)    a(t)    a(t)    a(t)           a(t); ...
       a(t)    a(t) -5*a(t)    a(t)    a(t)           a(t); ...
       b(t)    b(t)    b(t) -5*b(t)    b(t)           b(t); ...
       b(t)    b(t)    b(t)    b(t) -5*b(t)           b(t); ...
       a(t)    a(t)    a(t)    b(t)  5*b(t) -3*a(t)-6*b(t); ...
    ];
% the 6-by-6 matrix returned from the function T when it is called with 
% input 1:
result = T(1)
% get some element of the result (the result is the matrix returned from 
% calling the function T with input 1):
result(4,5)
% trying to do the same with the output of the function T called with 
% input 1 directly doesn't work in MATLAB (the output from T should be 
% stored in a variable first, i.e., 'result' here):
try
    T(1)(4,5);
catch ME
    disp(ME.message);
    % but you can index T(1) without storing in a variable, if you really
    % want to:
    subsref(T(1),substruct('()',{4,5}))
end