- #1
Dustinsfl
- 2,281
- 5
For a fixed number a, find the number of solutions $z^5+2z^3-z^2+z=a$ satisfying $\text{Re} \ z>0$.
Not to sure on how to tackle this one.
Not to sure on how to tackle this one.
dwsmith said:For a fixed number a, find the number of solutions $z^5+2z^3-z^2+z=a$ satisfying $\text{Re} \ z>0$.
Not to sure on how to tackle this one.
dwsmith said:$
z^5\left(1+\frac{2}{z^2}-\frac{1}{z^3}+\frac{1}{z^4}-\frac{a}{z^5}\right)
$ After you did this, what did you do for the argument? I don't understand.
chisigma said:According to the so called The 'argument principle', if f(*) is analytic in D and $\gamma$ is the 'frontier' of D, then the number of zeroes of f(*) in D is given by...
$\displaystyle n= \frac{1}{2\ \pi\ i}\ \int_{\gamma} \frac{f^{'}(z)}{f(z)}\ dz$ (1)
We consider $\displaystyle f(z)=z^{5}+2\ z^{3} -z^{2}+z-a$ and we set p the number of roots of f(*) with positive real part and q the number of roots of f(*) with negative real part. Of course is p+q=5. Now if we apply (1) and choose D as the 'big half circle tending to the left half plane' we obtain...
$\displaystyle q= \frac{1}{2\ \pi} \int_{- \infty}^{+ \infty} \frac{f^{'}(i\ y)}{f(i\ y)}\ dy = \frac{1}{2\ \pi} \int_{- \infty}^{+ \infty} \frac {(5\ y^{4} -6\ y^{2} +1) -2\ i\ y}{(y^{2}-a) +i\ (y^{5}-y^{3}+y)}\ dy$ (2)
The detail of computation of integral (2) are however 'a little complex' and that is 'postposed' to a successive post...
The Argument Principle is a mathematical theorem that is used to determine the number of zeros of a complex-valued function within a given region. It is based on the concept of the winding number, which measures how many times a function "wraps" around a point in the complex plane.
Yes, the Argument Principle can be applied to any complex-valued function, as long as it is analytic (i.e. differentiable) within the given region. This includes polynomials, rational functions, and other types of transcendental functions.
The Argument Principle is closely related to the Fundamental Theorem of Algebra, which states that every non-constant polynomial has at least one complex root. The Argument Principle provides a way to count the number of these roots within a given region.
The Argument Principle has various applications in engineering and physics, such as in the design and analysis of control systems, signal processing, and electrical circuits. It is also used in fluid dynamics and quantum mechanics to study the behavior of complex systems.
The Argument Principle is a powerful tool in complex analysis, but it does have some limitations. For example, it only applies to functions that are analytic within a given region, and it does not provide information about the location of the zeros, only the number of zeros. Additionally, it may not work for functions with singularities or branch cuts.