(second round) creating a certain type of matrix

I cleaned up your function a bit but please double check

 generate.matrix <- function(nr, runs=5){

   h   <- nr/2                                ## half of nr
   nc  <- nr/10 + 1

   mat <- matrix(0, nr, nc)                   ## initialize

   mat[ ,1] <- c( rep(1, h), rnorm(h) )       ## 1st column
   mat[ (h+1):(h+5), 2] <- rnorm(5)           ## 2nd column

   if( nc > 3 ){
    for (i in 3:nc){                          ## column 3 - end

      start <-  h + 5*(i-2) + 1
      end   <-  start + runs - 1

      mat[ start:end, i] <- rnorm( runs )    
    }
   }
   return(mat)
 } 

However you can simplify this greatly. If you ignore the first column
(which looks like some initialisation column in simulation process),
then you have a matrix with nr/2 rows and nr/10 columns with diagonal
blocks 5 runs filled with rnorm values. Here is what I propose :

 gen.mat <- function(x, runs=5){

   if( (x %% 2*runs)!=0 ) stop(x, " is not a multiple of ", 2*runs)

   nr  <- x/2                   
   nc  <- x/(2*runs)

   mat <- matrix(0, nr, nc)  
   for (i in 1:nc) mat[ ((i-1)*runs + 1) : (i*runs), i ] <- rnorm(runs)

   down <- cbind( rnorm(nr), mat )
   top  <- cbind( 1, matrix( 0, nr=nr, nc=nc ) )
   out  <- rbind( top, down )

   return(out)
 }

# Examples 
 gen.mat(50)
 gen.mat(55)         ## should generate an error
 gen.mat(24, runs=6)

Does this function do what you want to ?

Regards, Adai

(second round) creating a certain type of matrix

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