How can I find an specific value inside an array without using the find function?

Question

Pipe 2022-8-28

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评论： Walter Roberson 2022-8-28

I need to store the index when w>=10 in an array without using the find function. So for example in my code w=10 at t1 8. Is there any way to do that without using the find function?

array=zeros(2,2);
t=0:20;
i=2;
dwdt = @(t,w)(-2.*w+5.05.*w.^0.6);
[t,w] = ode45(dwdt,t,0.5);
%w=10 @ t= 8
index= find(w>=10);%dont use find function
array(i)= index(1);

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Walter Roberson 2022-8-28

What is the reason to avoid find()? There are ways to get indices in a vectorized way without using find() but they are not especially efficient for large matrices.

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Answer 1

Voss 2022-8-28

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https://ww2.mathworks.cn/matlabcentral/answers/1789250-how-can-i-find-an-specific-value-inside-an-array-without-using-the-find-function#answer_1036320

编辑：Voss 2022-8-28

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You can use the max function with second output argument, applied to the logical array w>=10, in order to return the first index where w>=10.

array=zeros(2,2);
t=0:20;
i=2;
dwdt = @(t,w)(-2.*w+5.05.*w.^0.6);
[t,w] = ode45(dwdt,t,0.5);
%w=10 @ t= 8
[~,index] = max(w>=10);
disp(index)
     8
array(i)= index(1);