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POStrassen's Algorithm Returning Zero
 

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    <p>The idea is to create a timer that will return how long it takes to perform a certain function. I sat and coded a matrix class and a <code>Strass</code> function that <em>should</em> multiply that I feed into it.</p> <p>The timer function works correctly in that it returns the time that it takes to execute the <code>Strass</code> function. However, the <code>Strass</code> function doesn't return a matrix that has been multiplied. It is a matrix of all zeroes. It's as if the <code>Strass</code> function isn't assigning anything to Matrix C. Ever.</p> <p>For example, multiplying a 2x2 matrix gives the following result:</p> <pre><code> 0.00 // P1 0.00 0.00 // the matrix after multiplication 0.00 0.00 7102000 // the time it took to do this </code></pre> <p>The <code>Strass</code> function looks like this:</p> <pre><code>public static void Strass(Matrix A, Matrix B, Matrix C) { // It has been suggested that P1-P7 should be of size // A.size()/2. Changing this does not fix the problem. Matrix P1 = new Matrix(A.size()); Matrix P2 = new Matrix(A.size()); Matrix P3 = new Matrix(A.size()); Matrix P4 = new Matrix(A.size()); Matrix P5 = new Matrix(A.size()); Matrix P6 = new Matrix(A.size()); Matrix P7 = new Matrix(A.size()); // if n = 1 then if (A.size() == 1) { C = A.times(B); } else { if (A.size() != B.size()) throw new RuntimeException("Somehow, the sizes of the matrices aren't equal."); int sizeOf = A.size(); // The ungodly recursive calls. Strass(A.partition(1, sizeOf/2, 1, sizeOf/2).plus(A.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), B.partition(1, sizeOf/2, 1, sizeOf/2).plus(B.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), P1); Strass(A.partition(sizeOf/2+1, sizeOf, 1, sizeOf/2).plus(A.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), B.partition(1, sizeOf/2, 1, sizeOf/2), P2); Strass(A.partition(1, sizeOf/2, 1, sizeOf/2), B.partition(1, sizeOf/2, sizeOf/2+1, sizeOf).minus(B.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), P3); Strass(A.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf), B.partition(sizeOf/2+1, sizeOf, 1, sizeOf/2).minus(B.partition(1, sizeOf/2, 1, sizeOf/2)), P4); Strass(A.partition(1, sizeOf/2, 1, sizeOf/2).plus(A.partition(1, sizeOf/2, sizeOf/2+1, sizeOf)), B.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf), P5); Strass(A.partition(sizeOf/2+1, sizeOf, 1, sizeOf/2).minus(A.partition(1, sizeOf/2, 1, sizeOf/2)), B.partition(1, sizeOf/2, 1, sizeOf/2).plus(B.partition(1, sizeOf/2, sizeOf/2+1, sizeOf)), P6); Strass(A.partition(1, sizeOf/2, sizeOf/2+1, 1).minus(A.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), B.partition(sizeOf/2+1, sizeOf, 1, sizeOf/2).plus(B.partition(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf)), P7); C.addPart(1, sizeOf/2, 1, sizeOf/2, (P1.plus(P4)).minus(P5.plus(P7))); C.addPart(sizeOf/2+1, sizeOf, 1, sizeOf/2, (P2.plus(P4))); C.addPart(1, sizeOf/2, sizeOf/2+1, sizeOf, (P3.plus(P5))); C.addPart(sizeOf/2+1, sizeOf, sizeOf/2+1, sizeOf, (P1.plus(P3)).minus(P2.plus(P3))); } } </code></pre> <p>I've tested the <code>addPart</code> function, and it is working correctly as far as I can tell. The same goes for the plus and minus functions. I did my best to go through and verify that I have all of the right sizes and numbers in all of the right locations, and I'm pretty darn sure that I do. So, somewhere in all of this, there is something amiss. </p> <p>For reference and brevity, I've pasted all of the relevant code <a href="http://pastebin.com/zSxA6jye" rel="nofollow">here</a>.</p>
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    1. CODo you have unit tests around your individual matrix methods to verify they are properly implemented?
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    2. COI've tested each of them, and they all seem to work just as I intend them too. I've obviously missed something, seeing as the whole thing doesn't work, but they *seem* to work just fine individually.
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