multiplying arrays

multiply_arrays.rb

# user_weights and user_predictions ordered by user_id, so that their weights and predictions match up.
user_weights = [.3, .2, .5]
user_predictions = [1.5, -1.0, 2.5]
result = 
# multiply each element in array by the matching element in the next array, then the sum  
# e.g. (.3*1.5)+(.2*-1)+(.5*2.5) = 1.5