Log Lines for Classes 5 and 6, STAT 705 Fall 2017
=================================================
9/13/2017

####   "sum" or "max" or "quantile"   have argument    na.rm   (default F)

### Timing run

rowsums = array(0, c(1e5,100))
Xmat = array(runif(1e7), c(1e5,1e2))      #### Note that the random-number generation 
                                     ### is now outside the timing runs.
ones = rep(1,100)

system.time({
      for(j in 1:100){ 	       
           for(i in 1:1e5) rowsums[i,j] = sum(Xmat[i,])
	     }   })
   user  system elapsed 
  10.54    0.00   10.55 

system.time({
      for(j in 1:100){ 
            rowsums[,j] = c(Xmat %*% ones)
	     }   })
   user  system elapsed 
   1.32    0.04    1.36          #### OK, so without the random-number generation the
                           ### actual computation of rowsums was 8 times as fast via linear algebra

####   now try this with other indexing parameters:

colsums = array(0, c(100,100))
ones2 = rep(1,1e5)

system.time({
      for(j in 1:100){ 
           for(i in 1:1e2) colsums[i,j] = sum(Xmat[,i])
	     }   })
   user  system elapsed 
   5.61    2.13    7.74 

system.time({
      for(j in 1:100){ 
           colsums[,j] = c(ones2 %*% Xmat)
	     }   })
   user  system elapsed 
   1.60    0.00    1.59       #### OK, without the random-number generation the
                           ### actual computation of colsums was 4 times as fast via linear algebra

  ##### SO IT IS A BIT QUICKER TO DO DO LINEAR ALGEBRA THAN FOR-LOOPS, 
  ##### BUT THE COMPARISON IS FAR LESS UNBALANCED THAN IN EARLIER VERSIONS OF R
  
  ##------------------------------------------------------------


## See Logs at  OldLogs/F16Logs, specifically Sep12F16.RLog and Sep14F16.RLog

## Compare the latter with:

> g = function(x,b) 2+7*x-b*x^2
  fmax2B = function(b) {
         bopt = optimize(g, c(0,10), maximum=T)
         unlist(bopt) }
 
 >  fmax2B(3)
Error in f(arg, ...) : argument "b" is missing, with no default

> b=3
  fmax2B(5)
  >   fmax2B(5)
Error in f(arg, ...) : argument "b" is missing, with no default