memory_test/memory_test.html

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      MEMORY_TEST - How Big Can Arrays Be?
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      MEMORY_TEST <br> How Big Can Arrays Be?
    </h1>

    <hr>

    <p>
      <b>MEMORY_TEST</b>
      is a C++ program which
      declares and uses a sequence of larger and larger arrays,
      to see what the memory limits are on a given computer.
    </p>

    <p>
      The program tries an increasing series of values of <b>N</b>, using
      powers of 2, between limits that you set.  At some point, the program
      may ask for more memory than can be provided, and crash.  This is one
      way to find out what the memory ceiling is!  The relevant power of 2
      is likely to be in the 20's:
      <table border="1">
        <tr>
          <th>Log(N)</th><th>N</th>
        </tr>
        <tr>
          <td>20</td><td>1,048,576</td>
        </tr>
          <tr>
          <td>21</td><td>2,097,152</td>
        </tr>
        <tr>
          <td>22</td><td>4,194,304</td>
        </tr>
        <tr>
          <td>23</td><td>8,388,608</td>
        </tr>
        <tr>
          <td>24</td><td>16,777,216</td>
        </tr>
        <tr>
          <td>25</td><td>33,554,432</td>
        </tr>
        <tr>
          <td>26</td><td>67,108,864</td>
        </tr>
        <tr>
          <td>27</td><td>134,217,728</td>
        </tr>
        <tr>
          <td>28</td><td>268,435,456</td>
        </tr>
        <tr>
          <td>29</td><td>536,870,912</td>
        </tr>
        <tr>
          <td>30</td><td>1,073,741,824</td>
        </tr>
      </table>
    </p>

    <p>
      Remember that your memory is probably described in terms of bytes,
      but that integers and reals require 4 bytes, and double precision reals
      require 8 bytes.
    </p>

    <h3 align = "center">
      Usage:
    </h3>

    <p>
      <blockquote>
        <b>memory_test</b> <i>log_n_min</i> <i>log_n_max</i>
      </blockquote>
      runs the program for sizes <b>N</b> = 2<sup>log_n_min</sup> to
      2<sup>log_n_max</sup>.
    </p>

    <h3 align = "center">
      Licensing:
    </h3>

    <p>
      The computer code and data files described and made available on this web page
      are distributed under
      <a href = "../../txt/gnu_lgpl.txt">the GNU LGPL license.</a>
    </p>

    <h3 align = "center">
      Languages:
    </h3>

    <p>
      <b>MEMORY_TEST</b> is available in
      <a href = "../../c_src/memory_test/memory_test.html">a C version</a> and
      <a href = "../../cpp_src/memory_test/memory_test.html">a C++ version</a> and
      <a href = "../../f_src/memory_test/memory_test.html">a FORTRAN90 version</a> and
      <a href = "../../m_src/memory_test/memory_test.html">a MATLAB version</a>.
    </p>

    <h3 align = "center">
      Related Data and Programs:
    </h3>

    <p>
      <a href = "../../cpp_src/linpack_bench/linpack_bench.html">
      LINPACK_BENCH</a>,
      a C++ program which
      measures the time needed to factor and solve a linear system.
    </p>

    <p>
      <a href = "../../f_src/machine/machine.html">
      MACHINE</a>,
      a FORTRAN90 library which
      can return various machine constants.
    </p>

    <p>
      <a href = "../../f_src/matmul/matmul.html">
      MATMUL</a>,
      a FORTRAN90 program which
      is an interactive matrix multiplication benchmark program.
    </p>

    <p>
      <a href = "../../f77_src/mdbnch/mdbnch.html">
      MDBNCH</a>,
      a FORTRAN77 program which
      is a benchmark code for a molecular dynamics calculation.
    </p>

    <p>
      <a href = "../../cpp_src/sum_million/sum_million.html">
      SUM_MILLION</a>,
      a C++ program which
      sums the integers from 1 to 1,000,000, as a demonstration of how
      to rate a computer's speed;
    </p>

    <p>
      <a href = "../../cpp_src/timer/timer.html">
      TIMER</a>,
      C++ programs which
      demonstrate how to compute CPU time or elapsed time.
    </p>

    <h3 align = "center">
      Source Code:
    </h3>

    <p>
      <ul>
        <li>
          <a href = "memory_test.cpp">memory_test.cpp</a>, the source code.
        </li>
        <li>
          <a href = "memory_test.sh">memory_test.sh</a>,
          commands to compile the source code.
        </li>
      </ul>
    </p>

    <h3 align = "center">
      Examples and Tests:
    </h3>

    <p>
      <ul>
        <li>
          <a href = "memory_test_output_g5.txt">memory_test_output_g5.txt</a>,
          a run of the program on a Mac G5,
          up to LOG(N) = 27.
        </li>
        <li>
          <a href = "memory_test_output_kachina.txt">memory_test_output_kachina.txt</a>,
          a run of the program on Kachina, an ALPHA workstation,
          up to LOG(N) = 27.
        </li>
      </ul>
    </p>

    <h3 align = "center">
      List of Routines:
    </h3>

    <p>
      <ul>
        <li>
          <b>MAIN</b> is the main program for MEMORY_TEST.
        </li>
        <li>
          <b>I4VEC_MEMORY_TEST</b> declares and uses an I4VEC of size N.
        </li>
        <li>
          <b>R4_CPU_TIME</b> reports the elapsed CPU time.
        </li>
        <li>
          <b>R4VEC_MEMORY_TEST</b> declares and uses an R4VEC of size N.
        </li>
        <li>
          <b>R8_CPU_TIME</b> reports the elapsed CPU time.
        </li>
        <li>
          <b>R8VEC_MEMORY_TEST</b> declares and uses an R8VEC of size N.
        </li>
        <li>
          <b>TIMESTAMP</b> prints the current YMDHMS date as a time stamp.
        </li>
      </ul>
    </p>

    <p>
      You can go up one level to <a href = "../cpp_src.html">
      the C++ source codes</a>.
    </p>

    <hr>

    <i>
      Last revised on 01 July 2009.
    </i>

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