So you effectively have different number of dx for each k? If so I'd do this something like this:
angleradian2 = nan([MaxNrRows,MaxNrCols]); % pre-allocate a nan-array with correct size
RCAr = angleradia2; % just make place for this one too
distance = RCAr; % and this one,
afstand = RCAr; % and this one...
for i1 = 1:length(RCA); % Changed k to i1 to get identifying label on loop-variable
...
...
afstand(i1,1:a) = thisData(1:a,1);
lengte = size(dx,1); % or 2 instead of 1, size returns a 2 (at least) element array with
% [sz1, sz2, ... szN] since you use this as an upper
% bound of your iteration it should be a scalar!
lengte = round(lengte);
for i2 = 1:lengte-1 % changed i to i2 for same reason as above AND keep i free for complex unit
P1 = [dx(i2), dy(i2), dz(i2)];
P2 = [dx(i2+1), dy(i2+1), dz(i2+1)];
angleradian2(i1,i2) = acos((P2(2)-P1(2)) / norm(P2-P1));
distance(i1,i2) = norm(P1 - P2);
end
RCAr(i1,:) = angleradian2(i1,:); %this point is not working
plot(afstand,angleradian2, '-')
hold on
end
HTH
