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POSpline Interpolation Performance in Scala vs Java
 

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  1. POSpline Interpolation Performance in Scala vs Java
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    <p>I translated <a href="http://commons.apache.org/math/api-2.2/src-html/org/apache/commons/math/analysis/interpolation/SplineInterpolator.html#line.53" rel="nofollow">this spline interpolation algorithm</a> from apache.commons.math from Java into Scala in the most straightforward way I could think of (see below). The function I ended up with runs 2 to 3 times slower than the original Java code. My guess is that the problem stems from the extra loops coming from the calls to <code>Array.fill</code>, but I can't think of a straightforward way to get rid of them. Any suggestions on how to make this code perform better? (It would also be nice to write it in a more concise and/or functional way -- suggestions on that front would be appreciated as well.)</p> <pre><code>type Real = Double def mySplineInterpolate(x: Array[Real], y: Array[Real]) = { if (x.length != y.length) throw new DimensionMismatchException(x.length, y.length) if (x.length &lt; 3) throw new NumberIsTooSmallException(x.length, 3, true) // Number of intervals. The number of data points is n + 1. val n = x.length - 1 // Differences between knot points val h = Array.tabulate(n)(i =&gt; x(i+1) - x(i)) var mu: Array[Real] = Array.fill(n)(0) var z: Array[Real] = Array.fill(n+1)(0) var i = 1 while (i &lt; n) { val g = 2.0 * (x(i+1) - x(i-1)) - h(i-1) * mu(i-1) mu(i) = h(i) / g z(i) = (3.0 * (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 i += 1 } // cubic spline coefficients -- b is linear, c quadratic, d is cubic (original y's are constants) var b: Array[Real] = Array.fill(n)(0) var c: Array[Real] = Array.fill(n+1)(0) var d: Array[Real] = Array.fill(n)(0) var j = n-1 while (j &gt;= 0) { c(j) = z(j) - mu(j) * c(j + 1) b(j) = (y(j+1) - y(j)) / h(j) - h(j) * (c(j+1) + 2.0 * c(j)) / 3.0 d(j) = (c(j+1) - c(j)) / (3.0 * h(j)) j -= 1 } Array.tabulate(n)(i =&gt; Polynomial(Array(y(i), b(i), c(i), d(i)))) } </code></pre>
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    1. COscala is built on top of java, so its not surprising that it will not be faster.
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      1. USAlexWien
    2. CONo, Scala is built on top of the JVM, and the compiler can emit JVM bytecode directly. Also, Scala is often the same speed as Java and, in some cases (e.g. when using specialization), is faster. However, to get code of equivalent speed, one sometimes has to write non-idiomatic Scala. I suggest the OP profile his code to see where the time is being spent in the Scala & Java code.
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      1. USnomad
 

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