Matrix-exponentiation operator: Difference between revisions

=={{header|Stata}}==

This implementation uses [https://en.wikipedia.org/wiki/Exponentiation_by_squaring Exponentiation by squaring] to compute a^n for a matrix a and an integer n (which may be positive, negative or zero).

<lang stata>real matrix matpow(real matrix a, real scalar n) {

real matrix p, x

real scalar i, s

s = n<0

n = abs(n)

x = a

p = I(rows(a))

for (i=n; i>0; i=floor(i/2)) {

if (mod(i,2)==1) p = p*x

x = x*x

}

return(s?luinv(p):p)

}</lang>

Here is an example to compute Fibonacci numbers:

<lang stata>: matpow((0,1\1,1),10)

[symmetric]

1 2

+-----------+

1 | 34 |

2 | 55 89 |

+-----------+</lang>