Suppose I enter a complex number, say z = (-2)*exp(i*pi/6). And, I have to get the phase of "z" as [pi/6] only. But when I try to retrieve the phase using angle(z), it would display the phase as [(pi/6)-pi]. I understand the reason behind shift of angle "pi" and I don't want this to happen in my original phase. Please help me out on this problem.
pi/6 is not the phase of z. It is the phase of z/-2. Thus angle(z/-2) = pi/6.
Notice that typically angle(exp(i*a)) not equal a. When equality holds depends on a convention built into the function angle (I don't know the convention that matlab uses).
Either angle(exp(i*a)) = a for all a in [0, 2*pi) or
angle(exp(i*a)) = a for all a in (-pi, pi]
(you know closed, open, and half-open intervals?)
You may consider the "four-quadrant inverse tangent ", i.e. try in matlab
z = -3 + 7i
Phi = atan2(imag(z),real(z)) % phase angle
@Yatish
I'm not sure that you posed the question that I and probably also Matthias answered. The words 'original phase' in your question hints to a programming context in which z is a complex variable that was initialized as z=exp(pi/6) and in some later program step was multiplied by -2 and (probably) will be multiplied by other factors in further steps. If these redefinitions of values of z are performed symbolically (i.e. in terms of analytic expressions) you can see the factor exp(pi/6) still as a part (sub-term) of the expression for the changed value. This may trigger the idea that it should be possible to get the original phase back somehow. This is an illusion however. The only (simple and safe) way to get hold of the 'original phase' is to store it in a separate variable. E.g.
z = exp(i*pi/6)
z0 = z
z=z*(-2)
...
print(z,z0) sorry, probably not true matlab.
BTW, would be nice to hear from you whether we toached your problem or missed it.
angle(r*exp(i*theta)) is equal to theta only if r is real positive number and (at least in MATLAB) theta lies between ±π.
I believe that with a formal calculation software tool such as Mapple, you can have good traceability
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