R help - Aug 2011 - Functions for Sum of determinants of ranges of matrix subsets

Dear R-help list,
Pls I have this problem. Suppose I have a matrix of size nxn say, generated as
follows
 
z<-matrix(rnorm(n*n,0,1),nrow=n)
 
I want to write a function such that for i in 1:n, I will remove the rows and
columns
corresponding to i (so, will be left with n-1*n-1 submatrix in each cases). Now
I need
the sum of the determinant of each of this submatrices. As an example, if n=3,
it means I will have det(1strow and 1stcolum removed) + det(2ndrow and 2ndcolum
removed) + det(3rdrow and 3rdcolum removed).
 
Any help will be appreciated. Thanks
 
John
	[[alternative HTML version deleted]]

Hi:

Try this:
> z <- matrix(rnorm(100), nrow = 10)
> sum(sapply(seq_len(nrow(z)), function(k) det(z[-k, -k])))
[1] 1421.06

where
> sapply(seq_len(nrow(z)), function(k) det(z[-k, -k]))
 [1]  432.11613   81.65449  516.95791   54.72775  804.32097 -643.35436
 [7] -411.15932  394.18780   84.13173  107.47665

HTH,
Dennis

On Tue, Aug 2, 2011 at 5:18 AM, john james <dntssa at yahoo.com>
wrote:
> Dear R-help list,
> Pls I have this problem. Suppose I have a matrix of size nxn say, generated
as follows
>
> z<-matrix(rnorm(n*n,0,1),nrow=n)
>
> I want to write a function such that for i in 1:n, I will remove the rows
and columns
> corresponding to i (so, will be left with n-1*n-1 submatrix in each cases).
Now I need
> the sum of the determinant of each of this submatrices. As an example, if
n=3, it means I will have det(1strow and 1stcolum removed) + det(2ndrow and
2ndcolum removed) + det(3rdrow and 3rdcolum removed).
>
> Any help will be appreciated. Thanks
>
> John
> ? ? ? ?[[alternative HTML version deleted]]
>
>
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