X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/kahina_paper1.git/blobdiff_plain/c42326ed2bebe65f1b51b355637cf4d89d70bbce..1df92e2629fef95f9b236c8d952d94c08f5f34a0:/paper.tex diff --git a/paper.tex b/paper.tex index a2102e7..1d70450 100644 --- a/paper.tex +++ b/paper.tex @@ -268,7 +268,7 @@ The initialization of a polynomial $p(z)$ is done by setting each of the $n$ com \subsection{Vector $Z^{(0)}$ Initialization} \label{sec:vec_initialization} -As for any iterative method, we need to choose $n$ initial guess points $z^{(0)}_{i}, i = 1, . . . , n.$ +As for any iterative method, we need to choose $n$ initial guess points $z^{0}_{i}, i = 1, . . . , n.$ The initial guess is very important since the number of steps needed by the iterative method to reach a given approximation strongly depends on it. In~\cite{Aberth73} the Ehrlich-Aberth iteration is started by selecting $n$ @@ -299,7 +299,7 @@ Here we give a second form of the iterative function used by Ehrlich-Aberth meth \begin{equation} \label{Eq:Hi} -EA2: z^{k+1}=z_{i}^{k}-\frac{\frac{p(z_{i}^{k})}{p'(z_{i}^{k})}} +EA2: z^{k+1}_{i}=z_{i}^{k}-\frac{\frac{p(z_{i}^{k})}{p'(z_{i}^{k})}} {1-\frac{p(z_{i}^{k})}{p'(z_{i}^{k})}\sum_{j=1,j\neq i}^{j=n}{\frac{1}{(z_{i}^{k}-z_{j}^{k})}}}, i=0,. . . .,n \end{equation} It can be noticed that this equation is equivalent to Eq.~\ref{Eq:EA}, @@ -321,8 +321,8 @@ With high degree polynomial, the Ehrlich-Aberth method implementation, as well as the Durand-Kerner implement, suffers from overflow problems. This situation occurs, for instance, in the case where a polynomial having positive coefficients and a large degree is computed at a -point $\xi$ where $|\xi| > 1$, where $|x|$ stands for the modolus of a complex $x$. Indeed, the limited number in the -mantissa of floating points representations makes the computation of p(z) wrong when z +point $\xi$ where $|\xi| > 1$, where $|z|$ stands for the modolus of a complex $z$. Indeed, the limited number in the +mantissa of floating points representations makes the computation of $p(z)$ wrong when z is large. For example $(10^{50}) +1+ (- 10^{50})$ will give the wrong result of $0$ instead of $1$. Consequently, we can not compute the roots for large degrees. This problem was early discussed in