释义 |
Logarithmic Spiral Evolute
| (1) |
Using
| (2) |
gives
and
so
and the Tangent Vector is given by
The coordinates of the Evolute are therefore
So the Evolute is another logarithmic spiral with , as first shown by Johann Bernoulli. However, in some cases, the Evolute is identical to the original, as can bedemonstrated by making the substitution to the new variable
| (9) |
Then the above equations become
which are equivalent to the form of the original equation if
| (12) |
| (13) |
| (14) |
where only solutions with the minus sign in exist. Solving gives the values summarized in the following table. | | | 1 | 0.2744106319... | | 2 | 0.1642700512... | | 3 | 0.1218322508... | | 4 | 0.0984064967... | | 5 | 0.0832810611... | | 6 | 0.0725974881... | | 7 | 0.0645958183... | | 8 | 0.0583494073... | | 9 | 0.0533203211... | | 10 | 0.0491732529... | |
ReferencesLauwerier, H. Fractals: Endlessly Repeated Geometric Figures. Princeton, NJ: Princeton University Press, pp. 60-64, 1991. |