[R] Strange R squared, possible error

[derek]

1) In my very humble opinion R^2 can't be negative, at least for data for
which it sound to use linear model.
Or the data would have to be utterly wrong to fit them with linear model.

2) I don't want to fit data with linear model of zero intercept.
3) I dont know if I understand correctly. Im 100% sure the model for my data
should have zero intercept. 
The only coordinate which Im 100% sure is correct. If I had measured quality
Y of a same sample X0 number of times I would get E(Y(X0))=0.

Basically what I need to compute is R^2=1- (sum(residue^2))/(sum(Y[i])) both
for model with and without intercept. I don't want to consider null model
(model with zero intercept) at all.

I don't know why to use y* in  R^2 = 1 - Sum(R[i]^2) / Sum((y[i]- y*)^2)

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