get new column using existing columns

I have to do two things

1. I have a 13 colums and from that i need to compute value and make new column i have tried to do it like this but it give only zerows for each raw
2. i need to save the file with the new column as 14 column data sheet

note: data set has about 1milion raws and 13 columns

the data is in a out put name Result2

Result2 = [D1, D2, D3, D4, D12, Ex, Az, Am, Te, IRR1, IRR2, IRR3, IRR4];

new colum i need is rat1

rat1 = (Result2(:,12). *2)/((Result2(:,11) + Result2(:,13))/2)

final output should be like below

Result3 = [D1, D2, D3, D4, D12, Ex, Az, Am, Te, IRR1, IRR2, IRR3, IRR4, rat1];

note since data file is two large this massage comes it asked to use matlab v7.3 or above please tel me the way i can generate the above Result3 file thank you verry mutch

[Dyuman Joshi]

Dot is missing for element wise division.

Also, since the data is quite large, directly append the data as the last column, rather than storing it.

Result2 = [D1, D2, D3, D4, D12, Ex, Az, Am, Te, IRR1, IRR2, IRR3, IRR4];
Result2 = [Result2 2*Result2(:,12)./(Result2(:,11) + Result2(:,13))/2];
%or
Result2(:,14)=2*Result2(:,12)./(Result2(:,11) + Result2(:,13))/2;

I think the latter would be faster.

[Amila]

Thank you very very mutch its working