Mercurial > hg > octave-lyh
changeset 11110:0be2d25700a7
polynomial/polyval.m: Use Horner's method.
| author | Marco Caliari <marco.caliari@univr.it> |
|---|---|
| date | Mon, 18 Oct 2010 20:13:45 +0200 |
| parents | 41d18f6342f9 |
| children | 84ad75921e35 |
| files | scripts/ChangeLog scripts/polynomial/polyval.m |
| diffstat | 2 files changed, 10 insertions(+), 3 deletions(-) [+] |
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--- a/scripts/ChangeLog +++ b/scripts/ChangeLog @@ -1,3 +1,7 @@ +2010-10-18 Marco Caliari <marco.caliari@univr.it> + + * polynomial/polyval.m: Use Horner's method. + 2010-10-18 John W. Eaton <jwe@octave.org> * plot/__go_draw_axes__.m: Always use gnuplot to display images.
--- a/scripts/polynomial/polyval.m +++ b/scripts/polynomial/polyval.m @@ -69,10 +69,11 @@ endif n = length (p) - 1; - k = numel (x); x = (x - mu(1)) / mu(2); - A = (x(:) * ones (1, n+1)) .^ (ones (k, 1) * (n:-1:0)); - y = A * p(:); + y = p(1); + for i = 2:n+1 + y = y .* x(:) + p(i); + endfor y = reshape (y, size (x)); if (nargout == 2) @@ -82,6 +83,8 @@ ## dy = t * sqrt (1 + sumsq (A/s.R, 2)) * s.normr / sqrt (s.df) ## If my inference is correct, then t must equal 1 for polyval. ## This is because finv (0.5, n, n) = 1.0 for any n. + k = numel (x); + A = (x(:) * ones (1, n+1)) .^ (ones (k, 1) * (n:-1:0)); dy = sqrt (1 + sumsq (A/s.R, 2)) * s.normr / sqrt (s.df); dy = reshape (dy, size (x)); endif