Square Root Complex Numbers

Question

Josh 2013-3-9

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评论： Yogan Sganzerla 2019-8-6

Hi

I'm new to Matlab. I have a matrix of data for example 1.04,-5.84,-5.84,8.54 etc. As you can see its a mixture of positive and negative values. I have to square root all the numbers and then add the square root up.

I get an output like this: 0 + 0.2572i 1.4758 0 + 1.0258i 0 + 1.0297i .... etc

How can I add these up because when I do the sum total is displayed like so: 24.1589 +25.8258i I was expecting a real number such as 25.0414 why is it formatted like this. I am new to matlab so not sure what I need to do, works fine if my data has no negative numbers so I assume it's to do with that.

Thanks

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Josh 2013-3-9

I'd expect 1.41421356i which I would get but say I have -2 and 4 (1.41421356i and 2) now if I add them up I get -2 + 1.41421356 I thought I'd get 0.58578644 though. If you can see were i'm coming from

Youssef Khmou 2013-3-9

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real parts are summed separately from imaginary parts , if you want add both Real and Imag sumsthen try :

 r=rand(10);
 p=sqrt(r);
 S=sum(real(p(:)))+sum(imag(p(:)));

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Answer 1

Youssef Khmou 2013-3-9

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hi Josh,

the square root of <0 number is complex number , if you only want the real part use "real" function, but if you want imaginary part, use "imag" function, and for the modulus you can use "abs" function , example :

 r=randn(10);
 p=sqrt(r);
 Real_part=sum(real(p(:)));
 Imag_part=sum(imag(p(:)));
 Modul_part=sum(abs(p(:)));

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Answer 2

Walter Roberson 2013-3-10

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编辑：Walter Roberson 2013-3-10

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To get the results you indicate you want (which are not the results one would normally want when taking the square roots of negative numbers),

sum(sqrt(r(r>0))) - sum(sqrt(-r(r<0)))

Remember, sqrt(-A) is not -sqrt(A) but is instead 1i * sqrt(A) where 1i indicates sqrt(-1)

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Torsten 2019-8-6

A = sqrtm(M)

Yogan Sganzerla 2019-8-6

Perfect! Thank you very much.

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