How to write a function with logical condition which takes an array and turns back an array?

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Bogdan MP 2021-10-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1570208-how-to-write-a-function-with-logical-condition-which-takes-an-array-and-turns-back-an-array

编辑： Matt J 2021-10-23

采纳的回答： Matt J

What I want to acheive is the following. Let's say I have the function

and

I have two vectors with nodes: x and y and I would like to calculate the function mentioned abose as an array. I can do it straightforwardly as

A = zeros(length(x), length(y));

for i = 1 : length(x)

for j = 1 : length(y)

if (x(i) ~= y(j))

A(i,j) = sin(alpha*(x(i) - y(j))) / (alpha * (x(i) - y(j)));

else

A(i,j) = 1;

end

This way is not really fast. I would like to have a function that will produce similar output as this cycle. More precisely, I would like to have the output in the form which is applicable for the trapz() command to calculate the double integral after all

trapz(y, trapz(x, K, 2))

there K has been calculated previously

I was trying something loke this

function val = K(alp, x, y)

% [x, y] = meshgrid(x, y); %% I was trying different variants here

% [x, y] = ndgrid(x, y);

if (x ~= y)

val = sin(alp * (x - y)) ./ ( alp * (x - y) );

else

val = 1;

end

but, of course, it did not work. Could you tell me, please, how shall I rewrite this function to achieve what I mentioned?

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采纳的回答

Matt J 2021-10-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1570208-how-to-write-a-function-with-logical-condition-which-takes-an-array-and-turns-back-an-array#answer_814883

在 MATLAB Online 中打开

K=sinc(alpha/pi*(x-y.'));

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Matt J 2021-10-23

编辑：Matt J 2021-10-23

在 MATLAB Online 中打开

x = (1:5) / pi;
y = (3:7) / pi;
K = sin(pi * (x - y.')) ./ ( pi * (x - y.') );
K(x == y.')=1       
K = 5×5
    0.4546    0.8415    1.0000    0.8415    0.4546
    0.0470    0.4546    0.8415    1.0000    0.8415
   -0.1892    0.0470    0.4546    0.8415    1.0000
   -0.1918   -0.1892    0.0470    0.4546    0.8415
   -0.0466   -0.1918   -0.1892    0.0470    0.4546