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who does logical works

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Faisal Al-Wazir
Faisal Al-Wazir 2022-3-19
评论： Star Strider 2022-3-19
>> x= [ 2 3 4 8 10 0 -2]
x =
2 3 4 8 10 0 -2
>> x(mod(x,2)==0)=5*x(mod(x,2)==0)
x =
10 3 20 40 50 0 -10
can someone explain x(mod(x,2)==0)=5*x(mod(x,2)==0)

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Star Strider
Star Strider 2022-3-19
Ran in:
The assignment:
x(mod(x,2)==0)=5*x(mod(x,2)==0)
finds numbers tthat are evenly divisible by 2 (so the remainder after division equals 0) and multiplies them by 5.
So:
x= [ 2 3 4 8 10 0 -2]
x = 1×7
2 3 4 8 10 0 -2
Lv = mod(x,2) == 0 % Select Elements Evenly Divisible By Zero
Lv = 1×7 logical array
1 0 1 1 1 1 1
x(Lv) = 5*x(Lv) % Multiply Them Bu 5
x = 1×7
10 3 20 40 50 0 -10
.
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Star Strider
Star Strider 2022-3-19
As always, my pleasure!

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John D'Errico
John D'Errico 2022-3-19
Ran in:
When something is too big or complicated, TAKE IT APART. TRY IT.
x= [ 2 3 4 8 10 0 -2]
x = 1×7
2 3 4 8 10 0 -2
So x is a vector of integers.
What does mod do?
mod(x,2)==0
ans = 1×7 logical array
1 0 1 1 1 1 1
This takes the modulus of each number, modulo 2. So it returns 0 for even numbers, 1 for odd numbers. What is on the right hand side of the equality? 5*x(mod(x,2)==0)
So what does x(a binary vector as we just created do? TRY IT!!!!!!!
This is a mask operation. It extracts the elements that correspond to 1. So essentially, it extracted oNLY the even elements of x.
x(mod(x,2)==0)
ans = 1×6
2 4 8 10 0 -2
Then what did it do? It multiplied them by 5.
5*x(mod(x,2)==0)
ans = 1×6
10 20 40 50 0 -10
Now what does the equality do there? It tells us to stuff those elements BACK into those same corresponding elements in x.
x(mod(x,2)==0)=5*x(mod(x,2)==0)
x = 1×7
10 3 20 40 50 0 -10
So put it all together. Take each even element of x. Multiply it by 5. Then stuff it back in place.
If something is too complicated, too big for you to understand. then take it apart. Look at only the small pieces. Then put it back together.
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Torsten
Torsten 2022-3-19
Can't you take it from the answer given ?
The elements of the x vector that are divisible by 2 and by 4 are set to 100, the other elements remain unchanged.
Since each number that is divisible by 4 is also divisible by 2, this is the same as
x(mod(x,4)==0) = 100
John D'Errico
John D'Errico 2022-3-19
Why is this starting to look like a homework ssignment to me?

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Torsten
Torsten 2022-3-19
The even elements of the x-vector are multiplied by a factor of 5, the odd elements remain unchanged.

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