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Diffstat (limited to 'tex/context/sample/math/math-knuth-dt.tex')
-rw-r--r-- | tex/context/sample/math/math-knuth-dt.tex | 29 |
1 files changed, 16 insertions, 13 deletions
diff --git a/tex/context/sample/math/math-knuth-dt.tex b/tex/context/sample/math/math-knuth-dt.tex index e32681437..7babcaf76 100644 --- a/tex/context/sample/math/math-knuth-dt.tex +++ b/tex/context/sample/math/math-knuth-dt.tex @@ -1,13 +1,16 @@ -{\bf 15.} (This procedure maintains four integers $(A, B, C, D)$ with the invariant meaning -that \quotation{our remaining job is to output the continued fraction for $(Ay + B)/(Cy + D)$, -where $y$ is the input yet to come.}) Initially set $j \leftarrow k \leftarrow 0$, $(A, B, C, D) \leftarrow (a, b, c, d)$; -then input $x_j$ and set $(A, B, C, D) \leftarrow (Ax_j + B, A, Cx_j + D, C)$, $j \leftarrow j + 1$, one or -more times until $C + D$ has the same sign as $C$. (When $j > 1$ and the input has not -terminated, we know that $1 < y < \infty$; and when $C + D$ has the same sign as $C$ we -know therefore that $(Ay + B)/(Cy + D)$ lies between $(A + B)/(C + D)$ and $A/C$.) -Now comes the general step: If no integer lies strictly between $(A + B)/(C + D)$ -and $A/C$, output $X_k \leftarrow \lfloor A/C \rfloor$, and set $(A, B, C, D) \leftarrow (C, D, A - X_ k C, B - X_k D)$, -$k \leftarrow k + 1$; otherwise input $x_j$ and set $(A, B,C, D) \leftarrow (Ax_j + B, A, Cx_j + D,C)$, -$j \leftarrow j + 1$. The general step is repeated ad infinitum. However, if at any time the -\emph{final} $x_j$ is input, the algorithm immediately switches gears: It outputs the continued -fraction for $(Ax_j + B)/(Cx_j + D)$, using Euclid's algorithm, and terminates. +{\bf 15.} (This procedure maintains four integers $(A, B, C, D)$ with the +invariant meaning that \quotation{our remaining job is to output the continued +fraction for $(Ay + B)/(Cy + D)$, where $y$ is the input yet to come.}) Initially +set $j \leftarrow k \leftarrow 0$, $(A, B, C, D) \leftarrow (a, b, c, d)$; then +input $x_j$ and set $(A, B, C, D) \leftarrow (Ax_j + B, A, Cx_j + D, C)$, $j +\leftarrow j + 1$, one or more times until $C + D$ has the same sign as $C$. +(When $j > 1$ and the input has not terminated, we know that $1 < y < \infty$; +and when $C + D$ has the same sign as $C$ we know therefore that $(Ay + B)/(Cy + +D)$ lies between $(A + B)/(C + D)$ and $A/C$.) Now comes the general step: If no +integer lies strictly between $(A + B)/(C + D)$ and $A/C$, output $X_k \leftarrow +\lfloor A/C \rfloor$, and set $(A, B, C, D) \leftarrow (C, D, A - X_ k C, B - X_k +D)$, $k \leftarrow k + 1$; otherwise input $x_j$ and set $(A, B,C, D) \leftarrow +(Ax_j + B, A, Cx_j + D,C)$, $j \leftarrow j + 1$. The general step is repeated ad +infinitum. However, if at any time the \emph{final} $x_j$ is input, the algorithm +immediately switches gears: It outputs the continued fraction for $(Ax_j + +B)/(Cx_j + D)$, using Euclid's algorithm, and terminates. |