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Last active Jul 20, 2017
A demo for an interface from sagemath to the LMFDB
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Created Oct 4, 2016
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Last active Aug 22, 2019
A note on cryptography
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Created Feb 26, 2015
View keybase.md

### Keybase proof

I hereby claim:

• I am davidlowryduda on github.
• I am davidlowryduda (https://keybase.io/davidlowryduda) on keybase.
• I have a public key whose fingerprint is B20D 472F F873 A4CF 8020 96D8 F4F4 C02B 336C 4F0A

To claim this, I am signing this object:

Created Jul 16, 2014
TeX to MSE for Will Jagy
View TeXtoMSEforWillFromMixedmath
 I wrote an article with Irving Kaplansky on indefinite binary quadratic forms, integral coefficients. At the time, I believe I used high-precision continued fractions or similar. It took me years to realize that the right way to solve Pell's equation, or find out the "minimum" of an indefinite form (and other small primitively represented values), or the period of its continued fraction, was the method of "reduced" forms in cycles/chains, due to Lagrange, Legendre, Gauss. It is also the cheapest way to find the class number and group multiplication for ideals in real quadratic fields, this probably due to Dirichlet. For imaginary quadratic fields, we have easier "reduced" positive forms. A binary quadratic form, with integer coefficients, is some $$f(x,y) = A x^2 + B xy + C y^2.$$ The discriminant is $$\Delta = B^2 - 4 A C.$$ We will abbreviate this by $$\langle A,B,C \rangle.$$ It is primitive if $latex {\gcd(A,B,C)=1. }$ Standard fact, hard to discover but easy to check:  (A x^2 + B x y + C D y
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