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Complex Number Manipulation

Let's run through a few elementary manipulations of complex numbers in Matlab:

>> x = 1; 
>> y = 2;
>> z = x + j * y

z =
   1 + 2i

>> 1/z

ans =
   0.2 - 0.4i

>> z^2

ans =
  -3 + 4i

>> conj(z)

ans =
   1 - 2i

>> z*conj(z)

ans =
     5

>> abs(z)^2

ans =
    5

>> norm(z)^2

ans =
    5

>> angle(z)

ans =
    1.1071

Now let's do polar form:

>> r = abs(z)

r =
    2.2361

>> theta = angle(z)

theta =
    1.1071

Curiously, $ e$ is not defined by default in Matlab (though it is in Octave). It can easily be computed in Matlab as e=exp(1).

Below are some examples involving imaginary exponentials:

>> r * exp(j * theta)

ans =
   1 + 2i

>> z

z =
   1 + 2i

>> z/abs(z)

ans =
   0.4472 + 0.8944i

>> exp(j*theta)

ans =
   0.4472 + 0.8944i

>> z/conj(z)

ans =
  -0.6 + 0.8i

>> exp(2*j*theta)

ans =
  -0.6 + 0.8i

>> imag(log(z/abs(z)))

ans =
    1.1071

>> theta

theta =
    1.1071

>>
Here are some manipulations involving two complex numbers:
>> x1 = 1;
>> x2 = 2;
>> y1 = 3;
>> y2 = 4;
>> z1 = x1 + j * y1;
>> z2 = x2 + j * y2;
>> z1

z1 =
   1 + 3i

>> z2

z2 =
   2 + 4i

>> z1*z2

ans =
 -10 +10i

>> z1/z2

ans =
   0.7 + 0.1i

Another thing to note about matlab syntax is that the transpose operator ' (for vectors and matrices) conjugates as well as transposes. Use .' to transpose without conjugation:

>>x = [1:4]*j

x =
        0 + 1i   0 + 2i   0 + 3i   0 + 4i

>> x'

ans =
        0 - 1i
        0 - 2i
        0 - 3i
        0 - 4i

>> x.'

ans =
        0 + 1i
        0 + 2i
        0 + 3i
        0 + 4i


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``Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition'', by Julius O. Smith III, W3K Publishing, 2007, ISBN 978-0-9745607-4-8.
Copyright © 2014-04-21 by Julius O. Smith III
Center for Computer Research in Music and Acoustics (CCRMA),   Stanford University
CCRMA