# [R] Matrix multiplications

peter dalgaard pdalgd at gmail.com
Sat May 21 22:29:12 CEST 2016

```I don't know if there is some sort of propagation delay, but the reason has already been given and multiple fixes suggested.

-pd

> On 21 May 2016, at 21:26 , george brida <george.brida at gmail.com> wrote:
>
> Roy,
>
> Yes, t(y-X %*% b) is the transpose of y-X %*% b. In principle the product
> of  t(y-X %*% b) *(y-X %*% b) is a scalar, I don't know why I have an error
> message after the following line:
>
> (t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X)))*solve(t(X)%*% X)
>
> Thanks
>
>
> On Sat, May 21, 2016 at 9:10 PM, Roy Mendelssohn - NOAA Federal <
> roy.mendelssohn at noaa.gov> wrote:
>
>>> 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
>>>
>>>
>>>
>>> Thank you
>>>
>>> George
>>>
>>>      [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> **********************
>> "The contents of this message do not reflect any position of the U.S.
>> Government or NOAA."
>> **********************
>> Roy Mendelssohn
>> Supervisory Operations Research Analyst
>> NOAA/NMFS
>> Environmental Research Division
>> Southwest Fisheries Science Center
>> ***Note new address and phone***
>> Santa Cruz, CA 95060
>> Phone: (831)-420-3666
>> Fax: (831) 420-3980
>> e-mail: Roy.Mendelssohn at noaa.gov www: http://www.pfeg.noaa.gov/
>>
>> "Old age and treachery will overcome youth and skill."
>> "From those who have been given much, much will be expected"
>> "the arc of the moral universe is long, but it bends toward justice" -MLK
>> Jr.
>>
>>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.

--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

```