[R] summation coding

[djbanana]

I would like to code the following in R: a1(b1+b2+b3) + a2(b1+b3+b4) +
a3(b1+b2+b4) + a4(b1+b2+b3)

or in summation notation: sum_{i=1, j\neq i}^{4} a_i * b_i

I realise this is the same as: sum_{i=1, j=1}^{4} a_i * b_i - sum_{i=j} a_i
* b_i

would appreciate some help.

Thank you.



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