Agree, it is ambiguous. Will try again....
 
Suppose I have the following
 
X<-matrix(c(1:20),nrow=4,byrow=T), hence this is a 4 by 5 matrix
Y<-matrix(c(2,4,6,8),ncol=1), and this is a 4 by 1 vector, each value denote y1, y2,y3, y4
 
Step 1 - write each row of X as a vector, so I have vectors t(x_1), t(x_2), t(x_3) and t(x_4)
 
Step 2 (inner product) ---- [prod(t(x_1) *x_2) + prod(t(x_1) *x_3) + prod(t(x_1) *x_4) ] *y1
 
Repeat for each row of X, that is 
 
   [prod(t(x_2) *x_1) + prod(t(x_2) *x_3) + prod(t(x_2) *x_4)] *y2
   [prod(t(x_3) *x_1) + prod(t(x_3) *x_2) + prod(t(x_3) *x_4)] *y3
   [prod(t(x_4) *x_1) + prod(t(x_4) *x_2) + prod(t(x_4) *x_3)] *y4
 
 
Hope this makes better sense ...
 
 
 
 
 

> by the remaining j rows

"remaining j rows"  ==? What is "j", Is it nrow(X)-1 ? An what sort of  
"multiplication by rows" do you mean? The inner product?

> multiplied by j y values (i.e sum( t(x_i) x_j y_j) )

"multiplied by j y values" ==? You defined Y but not y. Assuming that  
you meant Y values, then we are still left to speculate about which of  
the 5 Y values are suppose to be matched to the 3 rows of X.


>>> David Winsemius <dwinsemius@comcast.net> 2009/04/03 04:24 AM >>>
Generally unambiguous questions get answered quickly. Perhaps other  
readers are having the same difficulties I am experiencing. So let's  
try to parse what you are asking:

On Apr 2, 2009, at 8:26 AM, Kutlwano Ramaboa wrote:

> Hello
>
> This may have been answered elsewhere, and I have looked on the web,  
> but nothing helps. I am trying to do the following:
>
> X<-matrix(c(1:15),nrow=3,byrow=T)
> Y<-matrix(c(2,4,6,8,10),ncol=1)
>
> I need to sum the product of each row of X

"sum the product of each row"  ==?  sum(   prod(x[i, ] * ?

> by the remaining j rows

"remaining j rows"  ==? What is "j", Is it nrow(X)-1 ? An what sort of  
"multiplication by rows" do you mean? The inner product?

> multiplied by j y values (i.e sum( t(x_i) x_j y_j) )

"multiplied by j y values" ==? You defined Y but not y. Assuming that  
you meant Y values, then we are still left to speculate about which of  
the 5 Y values are suppose to be matched to the 3 rows of X.

>
>
> Hope this makes sense.

Not to me.

>
>
> Thanks in advance.
>
> Ps: how do I reference all the help that I have had from the R: team?

?citation

>
>
> [[alternative HTML version deleted]]

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

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