# Help aligning two vectors with one centred on zero.

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Jason on 25 Oct 2016
Commented: Chaya N on 25 Oct 2016
I have a set of x values:
x1=-31, -15.5, 0, 14.9,30.2
I know that the separation should be 15 (=pitch) so I want to plot x1 against xreal then do a fit and look at the largest deviation.
I can create:
xreal=Pitch*((1:numel(x1)));
But I can't figure out how to align them AROUND 0,e.g
xreal = -30, -15, 0 , 15, 30
then I can easily plot x1 against xreal and linearly fit.

LauraLee Austin on 25 Oct 2016
How about this, it should allow the location of 0 in x1 to change and the number of values in set x1 to be variable as well. if true
x1 = [-31, -15.5, 0, 14.9,30.2];
Pitch = 15;
idx = find(x1==0);
numel(x1)
xreal=(Pitch*(1-idx)):Pitch:(Pitch*(numel(x1)-idx));
Jason on 25 Oct 2016
Perfect, thankyou

Chaya N on 25 Oct 2016
Edited: Chaya N on 25 Oct 2016
xreal=Pitch*((1:numel(x1)) - ceil(numel(x1)/2))
Jason on 25 Oct 2016
doesn't this assume that the x1 values are symmetrical around 0. although shown in the example, this may not always be the case.
Chaya N on 25 Oct 2016
"...align them AROUND 0"

Matt J on 25 Oct 2016
xreal=xreal-mean(xreal);
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Matt J on 25 Oct 2016
Edited: Matt J on 25 Oct 2016
The mean of xreal would still be at zero. That is the only interpretation of the requirement "centered AROUND 0" that we can intuit from your post.
Jason on 25 Oct 2016