Peter

Well, the only advantage is that the vectors x and y don't necessarily have to be ordered in a row format, they can be multidimensional arrays. The internal function mydot can handle their dot products.

Otherwise you are right, there is no much difference.

The pcg matlab function is also an alternative.

Not sure what advantage of conjgrad over Matlab builtin function LSQR (where preconditioning is possible):

x = lsqr(@afun,b);
    
function y = afun(x,transp_flag)
        if strcmp(transp_flag,'transp')
            y = A'*x;
        else
            y = A*x;
        end
    end