[jira] [Created] (MATH-1530) Spline interpolation : Avoid recomputing indexes when possible

["Yassine Damerdji (Jira)" <ji...@apache.org>]

Yassine Damerdji created MATH-1530:
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             Summary: Spline interpolation : Avoid recomputing indexes when possible
                 Key: MATH-1530
                 URL: https://issues.apache.org/jira/browse/MATH-1530
             Project: Commons Math
          Issue Type: Improvement
            Reporter: Yassine Damerdji


In org.apache.commons.math4.analysis.interpolation.SplineInterpolator and in org.apache.commons.math4.analysis.interpolation.AkimaSplineInterpolator, many indices are recomputed many times.

Example :
{code:java}
for (int i = 1; i < n; i++) {
    g = 2d * (x[i+1] - x[i - 1]) - h[i - 1] * mu[i -1];
    mu[i] = h[i] / g;
    z[i] = (3d * (y[i + 1] * h[i - 1] - y[i] * (x[i + 1] - x[i - 1])+ y[i - 1] *   h[i]) / (h[i - 1] * h[i]) - h[i - 1] * z[i - 1]) / g;
}{code}

can be replaced by :

{code:java}
int i = 1;
int iPlusOne = 2;
int iMinusOne = 0;

while (i < n) {
    g[i] = 2d * (x[iPlusOne] - x[iMinusOne]) - h[iMinusOne] * mu[iMinusOne];
    mu[i] = h[i] / g[i];
    iMinusOne = i;
    i = iPlusOne;
    iPlusOne = iPlusOne + 1;
}
{code}

In my tests, I saved almost 2% of processing time with this optimization.





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