# PageRank

### From Wikimization

(Difference between revisions)

(New page: <pre> function s=csum(x) % CSUM Sum of elements using a compensated summation algorithm % % For large vectors, the native sum command in Matlab does not appear to % use a compensated summa...) |
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% David Gleich, Stanford University, 2008 | % David Gleich, Stanford University, 2008 | ||

- | + | shat=0; y=0; e=0; | |

for i=1:numel(x) | for i=1:numel(x) | ||

- | + | shat_old = shat; | |

+ | y = x(i) + e; | ||

+ | shat = shat_old + y; | ||

+ | e = (shat_old - shat) + y; | ||

end | end | ||

</pre> | </pre> |

## Revision as of 20:27, 17 February 2009

function s=csum(x) % CSUM Sum of elements using a compensated summation algorithm % % For large vectors, the native sum command in Matlab does not appear to % use a compensated summation algorithm which can cause significant round % off errors. % % This code implements a variant of Kahan's compensated summation algorithm % which often takes about twice as long, but produces more accurate sums % when the number of elements is large. % % See also SUM % % Example: % v=rand(1e7,1); % sum1 = sum(v); % sum2 = csum(v); % fprintf('sum1 = %18.16e\nsum2 = %18.16e\n', sum1, sum2); % David Gleich, Stanford University, 2008 shat=0; y=0; e=0; for i=1:numel(x) shat_old = shat; y = x(i) + e; shat = shat_old + y; e = (shat_old - shat) + y; end