Friday, December 04, 2009

Upgraded Mac Mini RAM to max 3GB using a cheese slicer to pry open the cover. Learned a trick to do modular arithmetic faster. What is 25 in mod 7? Find x such that 25-x is a multiple of 7. X is 4, so 25 is congruent to 4 mod 7. Now for positive values you could just do without that, but it gets useful with negative ones. What is -25 mod 7? Find x such that -25-x is multiple of 7. Closest multiple is -28, so x = 3. -25 is congruent to 3 mod 7. Helps with exercises about computing inverses of matrices in Z7.