zeldris's blog

By zeldris, history, 5 months ago, In English,

Hello. In the contest of my university fell the following problem: Given D (-1000 <= D <= 1000) the determinant of a 2x2 matrix, obtain the matrix that has this determinant and the 4 elements [a, b, c, d] such that a! = B! = C! = D and a, b, c, d! = 0

Any hint of how to do this without without O (n ^ 4)

 
 
 
 
  • Vote: I like it
  • +2
  • Vote: I do not like it

»
5 months ago, # |
Rev. 3   Vote: I like it +27 Vote: I do not like it

I don't really get what's the problem.

Det{{a, b}, {c, d}} = a*d — b*c

Det{{ka, b}, {kc, d}} = k*Det{{a, b}, {c, d}}

Find a,b,c,d with det = 1 (like {{5, 3}, {3, 2}} and multiply one line by d.

  • »
    »
    5 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Wow, I never would have thought of this. We have all been taught these identities in school, but I'm really impressed by your argument. Thanks a lot for your insight.