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Date: Mon, 09 Jun 2003 15:49:20 -0400
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Ideas for Ada 200X
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Date: 2003-06-09T15:49:20-04:00
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tmoran@acm.org wrote:
> Regardless, given your templates, could you use them to write a
> piece of code to "A = A+B;" and a piece to "A += B;" to show us
> how those look when you use the templates, and also how fast do
> they execute 10**7 times on 3x3 matrices of zeros?

I noticed an error in my previous posting; change M to N.

For A += B, we need to add to Matrix

     template <typename T>
     Matrix &operator+=(const T &r)
     {
         for (int i = 0; i < N; ++i)
             for (int j = 0; j < N; ++j)
                 data[i][j] += r(i,j);
         return *this;
     }

Having done that, we can do (warning - this is not exactly the
code that I compiled, so it may have errors)

     #include <time.h>
     #include <iostream>
     #include <ostream>
     int main()
     {
         Matrix<3> A, B;
         int i, j;
         for (i = 0; i < 3; ++i)
            for (j = 0; j < 3; ++j)
               A.data[i][j] = B.data[i][j] = 0;

         long t1b = time(0);
         for (i = 0; i < 100000000; ++i) A = A + B;
         long t1e = time(0);
	std::cout << "+  " << t1e - t1b << '\n';

         long t2b = time(0);
         for (i = 0; i < 100000000; ++i) A += B;
         long t2e = time(0);
	std::cout << "+= " << t2e - t2b << '\n';
     }

On my Sun workstation, using g++.5.8 (GCC) 3.2.2
and compiling with -O6, I get 11 seconds for "+"
and 7 seconds for "+=". Notice that this is for
one hundred million (10**8) iterations.