How to find the index of the first and last non-zero value of a vector ?

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Adnan Hayat 2020-12-14

编辑： Adnan Hayat 2020-12-15

Hello, I have a vector suppose a function f(x), such that

f(x)= ...0,0,0,0,0,0,0,0,5,6,7,4,3,5,6,7,8,0,0,0,0,0,0,0... and

x = 1,2,3,4,5,....

I don't know which command can I use to find those values of x for which the values of f(x) are 5 and 8 (i.e the first and last non-zero values)?

Daniel Pollard 2020-12-14

编辑：Daniel Pollard 2020-12-14

The built in command find sounds like what you need. The code could look something like

f = ...0,0,0,0,0,0,0,0,5,6,7,4,3,5,6,7,8,0,0,0,0,0,0,0...;
x_idx = find(f);
x = [x_idx(1), x_idx(end)];

where x is the positions of the first non-zero component and the last non-zero component.

Edit To correct a mis-type.

Rik 2020-12-14

Note that f_x=f(x);ind=[find(f_x,1,'first') find(f_x,1,'last')]; might be faster, as the JIT might be able to optimize this call.

Adnan Hayat 2020-12-15

编辑：Adnan Hayat 2020-12-15

Thank you both, I got my issue resolved :)

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