just start by preallocate some memory for C :
clear C C2 B
n=1000;
m=100;
A=rand(n,m)+rand(n,m)*1j;
tic
B=zeros(m);
for ii=1:n
B=A(ii,:)'*A(ii,:);
C(ii,:)=B(:).';
end
toc
tic
C2 = zeros(n,m*m);
for ii=1:n
C2(ii,:) = reshape(A(ii,:)'*A(ii,:),1,m*m);
end
toc
isequal(C,C2)
=>
Elapsed time is 21.619996 seconds. % without preallocation
Elapsed time is 0.464255 seconds. % with preallocation
