Getting an error:Left side must be a quaternion in subscripted assignment if right side is a quaternion.

I am getting this error while working with quaternion functions. What does it mean and how to resolve it??/

[KALYAN ACHARJYA]

Can you elaborate your problem?

[James Tursa]

Please show the code you are using, or a small sample of it, that produces the error.

[VINAY KUMAR SHARMA]

y(shft)= E*(exp(-mu*pi/2*a*([0:N-2 N-1+even])).' .*(E'*f(shft)));

using this equation where f and mu are quaternion. I tried multiple things but I am facing a problem that quaternion is supported by only one subscript.how can I index an imagein quaternion form.