[R] qr.solve and lm (SOLVED)

[Vladimir Eremeev]

Vladimir Eremeev wrote:
> 
> Dear R experts,
> 
> I have a Matlab code which I am translating to R in order to examine and
> enhance it.
> First of all, I need to reproduce in R the results which were already
> obtained in Matlab (to make sure that everything is correct).
> 
> There are some matrix manipulations and '\' operation among them in the
> code.
> 
> I have the following data frame
> 
>> ABS.df
>            Pro        syn             unk                 Chl                 
> Y                  Nh            V1
> [skip]
> 
>> qr.solve(ABS.df[,1:6],ABS.df[,7])
>        Pro        syn        unk        Chl          Y         Nh 
>  0.3877544  0.4282277  0.2221960 -0.8668715  0.2821082 -1.3696411 
> 
> This reproduces the Matlab's numbers 
> However, I used to lm, its syntax seems to me more clear.
> 
> ?lm says that it uses QR decomposition to fit the model.
> Trying it:
> 
>>  coef(lm(V1~Pro+syn+unk+Chl+Y+Nh,data=ABS.df))
>  (Intercept)          Pro          syn          unk          Chl           
> Y           Nh 
>  0.001640184  0.417253116  0.351472810  0.196977369 -0.899729874 
> 0.265585292 -1.181526491 
> 
> Numbers differ.
> Obviously, I don't understand something. 
> Please, could you clarify, what?
> Thank you.
> 
> 

This was because of implied intercept term.

> lm(V1~Pro+syn+unk+Chl+Y+Nh+0,data=ABS.df)

Call:
lm(formula = V1 ~ Pro + syn + unk + Chl + Y + Nh + 0, data = ABS.df)

Coefficients:
    Pro      syn      unk      Chl        Y       Nh  
 0.3878   0.4282   0.2222  -0.8669   0.2821  -1.3696  

That is, reproduces earlier results.
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