Correlation is similar to convolution except that one does not need to flip an input about the origin (but correlation needs taking the complex conjugate of one of the operands), so for 3D real matrices, you can use convn(x3d,y3d(end:-1:1,end:-1:1,end:-1:1)) to compute 3D cross correlation.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
