Complex Numbers: The Phase of a Complex Number

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SUMMARY

The phase of a complex number represented as a = C * exp(i φ) is defined as φ when C > 0. However, the phase is not uniquely defined due to the periodic nature of the exponential function, leading to the equivalence C * exp(i φ) = C * exp(i(φ + 2πn)) for any integer n. To resolve this ambiguity, the phase can be defined within a coset φ + 2πℤ or constrained to intervals such as [0, 2π) or [-π, π). For C < 0, the phase must incorporate the sign of C, resulting in a phase of φ + π. When C = 0, the phase is undefined.

PREREQUISITES
  • Understanding of complex numbers and their representation
  • Familiarity with exponential functions and Euler's formula
  • Knowledge of periodic functions and their properties
  • Basic grasp of cosets and interval notation
NEXT STEPS
  • Study the properties of complex numbers in polar form
  • Learn about Euler's formula and its applications in complex analysis
  • Explore the concept of periodicity in trigonometric and exponential functions
  • Investigate the implications of complex phases in signal processing
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Mathematicians, physicists, engineers, and students studying complex analysis or signal processing who need a clear understanding of the phase of complex numbers.

pamparana
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I just wanted to check something. If I have a complex number of the form

a = C * \exp(i \phi)

where C is some non-complex scalar constant. Then the phase of this complex number is simply \phi. Is that correct?
 
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pamparana said:
I just wanted to check something. If I have a complex number of the form

a = C * \exp(i \phi)

where C is some non-complex scalar constant. Then the phase of this complex number is simply \phi. Is that correct?
If ##C > 0## then this is almost correct. However, the phase is not well-defined under this definition, because ##C\exp(i\phi) = C\exp(i(\phi+2\pi n))## for any integer ##n##. You can get around this by defining the phase to be the coset ##\phi + 2\pi \mathbb{Z}## or by constraining it to be in the interval ##[0,2\pi)## or ##[-\pi, \pi)## or some other half-open interval of length ##2\pi##.

If ##C < 0##, then you need to absorb the sign of ##C## into the phase:
$$a = -|C|\exp(i \phi) = |C|\exp(i(\phi + \pi))$$

If ##C = 0## then the phase is undefined.
 
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Thank you for this detailed answer!
 

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