conv2() vs filter2()

filter2做的是相关correlation，conv2做的是卷积convolution，卷积是会将模板翻转，而相关不会，具体看下面的例子

a = magic(5)a =17    24     1     8    1523     5     7    14    164     6    13    20    2210    12    19    21     311    18    25     2     9g = [0 0; 0 1];filter2(g,a,'full')ans =17    24     1     8    15     023     5     7    14    16     04     6    13    20    22     010    12    19    21     3     011    18    25     2     9     00     0     0     0     0     0filter2(g,a,'valid')ans =5     7    14    166    13    20    2212    19    21     318    25     2     9f = [1 0; 0 0]; %翻转后的模板filter2(f,a,'full')ans =0     0     0     0     0     00    17    24     1     8    150    23     5     7    14    160     4     6    13    20    220    10    12    19    21     30    11    18    25     2     9filter2(f,a,'valid')ans =17    24     1     823     5     7    144     6    13    2010    12    19    21