MATLAB: Can this be accelerated

Hi,

The following computations are very expensive for large matrices A, B and the coefficient q.

C=reshape(A,a1*q,b1)*B;
C=reshape(C,a1,b2*q);

a1 and a2 are the dimensions of A, while b1 and b2 are the dimensions of B and with the restriction that a2=b1*q.

In my applications, matrices A and B can have dimensions in the orders of thousands or more.

There is one way of implementing these operations using loops

C=zeros(a1,b2*q);
acols=0:q:(b1-1)*q;
ccols=0:q:(b2-1)*q;
for ii=q:-1:1
    C(:,ccols+ii)=A(:,acols+ii)*B;
end

but that strategy is not as fast as the one above. Is there any way to accelerate these operations?

try them for instance with the following

b1=1300;
b2=500;
q=350;
a1=300;
a2=b1*q;
B=rand(b1,b2);
A=rand(a1,a2);

Thanks