Major Description
It would be useful to have simple accumulator classes in Summation and LinearCombination to perform extended precision operations on arbitrary collections of values without requiring conversion to double[]. Ex:
Summation.Accumulator sum= Summation.accumulator(1d);
sum.add(x)
.add(y)
.add(z)
.add(w);
double sumResult = sum.get();
LinearCombination.Accumulator comb = LinearCombination.accumulator(1d);
comb.add(x, scale)
.add(y, scale)
.add(z, scale)
.add(w, scale);
double combResult = comb.get();
