You don't need to loop to generate the values that you multiply by +1i or -1i and pass into exp.
% Sample data
x = randn(4, 5, 6);
y = 1:6;
% Approach 1: element-wise multiplication
z1 = x.*reshape(y, 1, 1, size(x, 3));
% Approach 2: loops
z2 = zeros(size(x));
for r = 1:size(x, 1)
for c = 1:size(x, 2)
for p = 1:size(x, 3)
z2(r, c, p) = x(r, c, p)*y(p);
end
end
end
% Check
z1-z2 % Should contain all 0's or small magnitude values
