如何在MATLAB中了解变量的大小

Question

我在MATLAB中有变量,我已经检查了它们的类,class()但我也想知道它们在内存中的大小.更准确地说,我知道它们是双重类型,我想确保它们是32位双精度而不是64位.

我正在使用的MATLAB版本是R2009b.

Answer 1

您可以使用whos来获取一组结构,这些结构描述了每个变量的字节大小.

请注意,根据定义,double是64位!

Answer 2

我写了一个简单的便利函数来处理这个问题.用法是:

>> x = ones(1000);
>> ByteSize(x)
7.63 Mb

我运行R2007a,因此Java对象不返回大小的问题可能已在后续版本中修复.这是代码:

function ByteSize(in, fid)
% BYTESIZE writes the memory usage of the provide variable to the given file
% identifier. Output is written to screen if fid is 1, empty or not provided.

if nargin == 1 || isempty(fid)
    fid = 1;
end

s = whos('in');
fprintf(fid,[Bytes2str(s.bytes) '\n']);
end

function str = Bytes2str(NumBytes)
% BYTES2STR Private function to take integer bytes and convert it to
% scale-appropriate size.

scale = floor(log(NumBytes)/log(1024));
switch scale
    case 0
        str = [sprintf('%.0f',NumBytes) ' b'];
    case 1
        str = [sprintf('%.2f',NumBytes/(1024)) ' kb'];
    case 2
        str = [sprintf('%.2f',NumBytes/(1024^2)) ' Mb'];
    case 3
        str = [sprintf('%.2f',NumBytes/(1024^3)) ' Gb'];
    case 4
        str = [sprintf('%.2f',NumBytes/(1024^4)) ' Tb'];
    case -inf
        % Size occasionally returned as zero (eg some Java objects).
        str = 'Not Available';
    otherwise
       str = 'Over a petabyte!!!';
end
end

Answer 3

dt=whos('VARIABLE_YOU_CARE_ABOUT'); MB=dt.bytes*9.53674e-7;  

这将为您提供以兆字节为单位的大小,例如MB = 123.78