What is the Number of Complex Roots for the Given Equation with Varying d?

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Discussion Overview

The discussion centers on determining the number of complex roots for the equation (2 z^2 + 1)^2 ((z + d)/(z - i))^1/2 - (2 z^2 - d)^2 ((z + i)/(z - d))^1/2 == 0, particularly as the parameter d varies within the range 0 < d < 1. Participants explore the implications of this equation in terms of complex analysis and the argument principle.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about the number of complex roots and suggests using the argument principle to analyze how the number varies with d.
  • Another participant notes that simplification leads to a fourth-degree equation in z^2, indicating a maximum of 8 possible roots.
  • A subsequent reply questions which of these roots are actual zeros of the original equation, highlighting a concern about the validity of the roots obtained.
  • A later participant reports numerical findings indicating that for small values of d, only four roots (two real and two purely imaginary) are present, while for larger d, two additional complex conjugate roots emerge. They seek analytical methods to determine the critical value of d at which this change occurs.

Areas of Agreement / Disagreement

Participants express differing views on the nature and number of roots, with some suggesting a maximum potential number while others provide numerical evidence of varying root types based on the value of d. The discussion remains unresolved regarding the analytical determination of critical values.

Contextual Notes

The discussion involves assumptions about the behavior of roots as d changes, and the dependence on numerical methods versus analytical approaches is noted. There are unresolved questions regarding the classification of roots as valid solutions to the original equation.

eradi
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How many complex roots admit the following equation:
(2 z^2 + 1)^2 ((z + d)/(z - i))^1/2 - (2 z^2 - d)^2 ((z + i)/(z - d))^1/2 == 0
for 0 < d < 1, where i = (-1)^1/2.
Can I found how their number varies with d by using the argument principle?
Thanks in advance for helpfull suggestions
 
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You get a fourth deg. equation in z^2 equation on simplification, so a maximum of 8 zeroes is possible.
 
Yes, but which of them are actually zeroes of the starting equation?
Thanks for your interest
 
I found numerically that for small d only four roots are admissible (two reals and two purely imaginary) but for large d two more complex conjugate roots appear.
There exists any analitical tools to define this critical value of d?
 

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