HI everyone!<br>  I have tried to install graph_tool by compiling source code.But for many times , it reports:<br>              virtual memory exhausted: Cannot allocate memory<br>  My PC has a 4G main memory and Intel i5 CPU.I thought 4G is enough.<br>
<br>  Then I tried to install by apt-get, and came up with a problem.<br>  I have already installed these library before, and versions are right. <br><br> graph-tool : Depends: libboost-iostreams1.42.0 (&gt;= 1.42.0-1) but it is not installable<br>
              Depends: libboost-python1.42.0 (&gt;= 1.42.0-1) but it is not installable<br>              Depends: libboost-regex1.42.0 (&gt;= 1.42.0-1) but it is not installable<br>              Depends: libcgal5 but it is not installable<br>
              Depends: libpython2.6 (&gt;= 2.6) but it is not installable<br>              Depends: libboost1.42-dev but it is not installable<br><br>  Can anyone help me ? <br>  By the way,how to use the public key ? <br>
  I have tried &quot;apt-key add signature.asc&quot;,but it reports: <br>              gpg: no valid OpenPGP data found.<br><br><br>