[R] Matrix multiplications

[Roy Mendelssohn - NOAA Federal]

>  str(t(y-X %*% b))
 num [1, 1:10] 0.595 -1.7538 -0.0498 -1.651 -0.6328 ...
> str((y-X %*% b))
 num [1:10, 1] 0.595 -1.7538 -0.0498 -1.651 -0.6328 …

-Roy


> On May 21, 2016, at 12:00 PM, george brida <george.brida at gmail.com> wrote:
> 
> Dear R users:
> 
> I have written the following lines :
> 
>> x=c(10,11,12,13,14,17,15,16,10,11,41,25,26,14,12,14,15,20,14,22)
>> x=matrix(x,ncol=2)
>> a=matrix(1,nrow(x),1)
>> X=cbind(a,x)
>> y=c(12.00, 11.00, 13.00, 12.50, 14.00, 18.50, 15.00, 12.50, 13.75, 15.00)
> 
>> b=solve(t(X)%*% X)%*% t(X)%*% y
> 
> when I wrote the following line
>> (t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X)))*solve(t(X)%*% X)
> I have obtained an error message, I don't know why namely (t(y-X %*%
> b)%*%(y-X %*% b)/(length(y)-ncol(X))) is a scalar:
>> (t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X)))
>         [,1]
> [1,] 3.620354
> 
> 
> Can you please help me.
> 
> Thank you
> 
> George
> 
> 	[[alternative HTML version deleted]]
> 
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**********************
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**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
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e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/

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