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# Lab for Automated Reasoning and Analysis LARA

# Differences

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non-converging_iteration_in_reals [2007/04/15 19:10] vkuncak |
non-converging_iteration_in_reals [2015/04/21 17:50] (current) |
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\begin{equation*} | \begin{equation*} | ||

\begin{array}{l} | \begin{array}{l} | ||

- | f : [0,2] \to [0,2] \\[1ex] | + | f : [0,2] \to [0,2] \\begin{equation*}1ex] |

f(x) = \left\{\begin{array}{rl} | f(x) = \left\{\begin{array}{rl} | ||

- | \displaystyle\frac{1+x}{2}, & x < 1 \\[2ex] | + | \displaystyle\frac{1+x}{2}, & x < 1 \\begin{equation*}2ex] |

\displaystyle \frac{3+2x}{4}, & x \geq 1 \end{array}\right. | \displaystyle \frac{3+2x}{4}, & x \geq 1 \end{array}\right. | ||

\end{array} | \end{array} | ||

Line 14: | Line 14: | ||

Start from e.g. x=1/2. Obtain a series converging to 1, but 1 is not a fixed point because $f(1)=5/4$. | Start from e.g. x=1/2. Obtain a series converging to 1, but 1 is not a fixed point because $f(1)=5/4$. | ||

- | This is because $f$ is not continuous. | + | This is because $f$ is not continuous. If it was continous (at least, continuous from the left), we would have the desired property. |

Whenever we converge to some $x^*$, we take $f(x^*)$ and continue iterating and taking limits (the "number of times" to iterate, even if infinite, depends on the size of the lattice, which can be formalized [[wk>ordinal number]]s). | Whenever we converge to some $x^*$, we take $f(x^*)$ and continue iterating and taking limits (the "number of times" to iterate, even if infinite, depends on the size of the lattice, which can be formalized [[wk>ordinal number]]s). | ||