Timeline for Action of birational map $f$ on the divisor class of line $[H]$
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
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| Jan 28, 2019 at 14:41 | vote | accept | Soby | ||
| Jan 27, 2019 at 21:19 | answer | added | Jérémy Blanc | timeline score: 1 | |
| Jan 18, 2019 at 4:05 | history | edited | Soby | CC BY-SA 4.0 |
added 44 characters in body
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| Jan 17, 2019 at 14:36 | comment | added | user47305 | One way is to find the degree is to simply write down the formula for $f$: you can find this in Dolgachev's book "Classical Algebraic Geometry" (it's on page 301 in my edition). Another method would be to argue that it lifts to a regular (and not merely birational) involution on the blow-up at the base points, and then the fact that the pushforward preserves the canonical class lets you compute the degree. | |
| Jan 17, 2019 at 14:29 | comment | added | YCor | Some context can be helpful. The underlying group is the Cremona group in dimension 2 (over an algebraically closed field, maybe of characteristic zero). The induced isometry $f_*$ is on the Picard-Manin space. | |
| Jan 17, 2019 at 14:27 | history | edited | YCor | CC BY-SA 4.0 |
fixed typo, added tag
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| Jan 17, 2019 at 12:01 | history | asked | Soby | CC BY-SA 4.0 |