[R] Re: matrix exponential: M0

[Vicente Canto Casasola]

H i, all!

First of all, I'd like to apologize for my poor English. It's for years 
I don't use it.

This is a R-version of a function I wrote a long ago for my HP48 calculator.
It works with the binary expression of the power and just need to 
duplicate the mem used by X.


Hope this helps.

mtx.exp<-function(X,n)
#Function to calculate the n-th power of a matrix X;
{
phi <- diag(rep(1,length(X[1,])))
pot <- X #This is the first power of the matrix.

while (n > 0)
  {
  if (n%%2)
    {
    phi <- phi%*%pot;
    }
    n <- n%/%2;
    pot <- pot %*% pot;
  }
return(phi);
}



#Here is some output:

 > xx <- matrix(c(1,0,1,1),2,2)
 > xx
     [,1] [,2]
[1,]    1    1
[2,]    0    1
 > mtx.exp(xx,3)
     [,1] [,2]
[1,]    1    3
[2,]    0    1
 > mtx.exp(xx,4)
     [,1] [,2]
[1,]    1    4
[2,]    0    1
 > mtx.exp(xx,6)
     [,1] [,2]
[1,]    1    6
[2,]    0    1
 > mtx.exp(xx,10)
     [,1] [,2]
[1,]    1   10
[2,]    0    1
 > mtx.exp(xx,1000)
     [,1] [,2]
[1,]    1 1000
[2,]    0    1


Vicente D. Canto Casasola