Create many new matrices from a larger matrix - r

Question

I am relatively new to R, though I have done a good amount of simple R programming. I think this should be an easy question but I can't seem to figure it out.
Updated:
The situation is that I need to fragment my data for regression analysis due to memory constraints on my computer. I essentially have three matrices that are pertinent call them X (n x k), y (n x 1), and Om ( n x n) I need to break these three matrices up by rows multiply them together in various ways and then add up the results. because of the error structure of Om some groups have to be rows of 3, others rows of 2 and others rows of 1. For a group of 3 we would have:
Xi (3 x k), yi (3 x 1) and Om3 (3 x 3)
I have Om1, Om2, and Om3 already build in R
Om1<-matrix(2)
vec1<-c(2,-1)
vec2<-c(-1,2)
Om2<-rbind(vec1,vec2)
vec3<-c(2,-1,0)
vec4<-c(-1,2,-1)
vec5<-c(0,-1,2)
Om3<-rbind(vec3,vec4, vec5)
Now the Question is how can I break up X, and y so that I can match the rows of X, y and Om. I was thinking I would need a loop but cannot get it to work something like:
for(i in 1:280){
assign(paste("xh", i, sep = ""), i)
}
for(i in 1:145){
xhi<- X[i,]
}
for(i in 146:195){
xhi<-X[ seq( from=i , length=2) , ]
}
for(i in 196:280){
xhi<-X[ seq( from=(i+49) , length=3) , ]
}
Where the first 145 xi 's correspond to Om1, the next 50 xi's correspond to Om2...I was thinking I would need a way to index them that was the same as eventually i need to sum up a product of xi, yi and Omi across i's
Sorry for the long post trying to be thorough, any advice would be greatly appreciated

Answer 1

Assume this matrix is named mtx, you want 10 such matrices of increasing row count, and that it has at least 55 rows, since the sum of the lengths that grow by one with each iteration is n(n+1)/2:
mlist <- list()
for (x in 1:10) mlist[[x]] <-mtx[ seq( from=x*(x-1)/2+1 , length=x) , ]
If the desire is as Carl suggests it would be:
mlist <- list()
for (x in 1:10) mlist[[x]] <-mtx[ seq( from=1 , length=x) , ]
Or:
mlist <- list()
for (x in 1:10) mlist[[x]] <-mtx[ seq( from=x , length=2) , ]