A Doubly Self Compensated Sum algorithm
s = accsum_fdcs ( x ) [s,e] = accsum_fdcs ( x )
a m-by-n, matrix of doubles
a 1-by-1 matrix of doubles, the highest significant digits of the sum
a 1-by-1, matrix of doubles, the lowest significant digits of the sum
A Doubly Self Compensated Sum algorithm. Uses the fasttwosum algorithm. This is a fast implementation, based on compiled source code. The input data x must be ordered in decreasing magnitude. To do this, we may use the accsum_order function with order=5.
"Stability and numerical accuracy of algorithms", Nicolas Higham
"Handbook of Floating Point Computations", Muller et al
https://hpcrd.lbl.gov/SCG/ocean/NRS/ECMWF/img14.htm
https://hpcrd.lbl.gov/SCG/ocean/NRS/SCSsum.F