[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

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