9A. Matrix Algebra

m0=: I=: =@i.@#

Identity matrix of order of y

m1=: inv=: %. 

Matrix inverse

d2=: mq=: %.

Matrix quotient

d3=: mp=: +/ . *

Matrix product

d4=: amp=: -/ . *

Alternating matrix product

m5=: det=: -/ . *

Determinant

d6=: fit=: {:@] %. {.@] ^/ i.@[

d fit x,:f x is coeffs of pn fit of degree d-1