没有matlab，用octave跑了跑，每个内循环大概花4秒多，用时比较稳定，没有越来越慢：

xy_2d=randn(8192,8192);
z_2d=randn(800,900);

u2 = ones(8192, 8192);

l_c = cputime();

for ite1 = 1:800
    for ite2 = 1:900
       u = exp(i.*sqrt(xy_2d- z_2d(ite1,ite2)));
       u2 = u2.*u;

       c_c = cputime ();
       printf("%f\n", c_c - l_c);
       l_c = c_c;
    end
end

$ octave a.m

octave: X11 DISPLAY environment variable not set
octave: disabling GUI features
4.765148
4.862631
4.779450
5.041904
4.884259
4.147731
4.518169
4.276477
3.707727
4.330566
4.823088
4.806313
4.823238
4.885304
4.861114
4.953960
3.853307
4.220949
4.907371
3.995417
4.943422
4.870499
3.797168
4.689785
4.807867

【 在 novicer 的大作中提到: 】
: u2 = exp(i.*zeros(8192,8192));
: for ite1 = 1:800
:    for ite2 = 1:900
: ...................
--
FROM 173.38.117.*