1) Your final else conditional is not working as you intend it to, but not for the reasons you think. MATLAB is not reading it as else means "if all the other conditions fail". What you want there is another elseif. What I'd suggest is replacing that else with an elseif and then putting an else AFTER that with some sort of error or warning message.
I think what's going on is you're actually FAILING all the other conditionals and because of the mistake with this line, you're missing that.
2) Is that first conditional as you intend? It reads as:
if pltvar1srt(i) == x2634(1,11) && x2634(1,16)
Is x2634(1,16) a logical? Because the way it reads here is as two separate conditions:
a) is pltvar1srt(I) == x2634(1,11)
b here will always read as true, unless x2634(1,16) == 0. You can try this in a shell simply by doing something like:
I suspect you meant for something like:
if (pltvar1srt(i) == x2634(1,11)) && (pltvar1srt(i) == x2634(1,16))
Also is x2634 a 2D matrix? Do you mean for it to be x2634(i,11)?
3) I'm confused as to the dimensions of pltvar1srt. Is it a 2D vector or a 1D vector? The conditionals pltvar1srt(:,2) imply it's 2D but that doesn't seem to be what you're describing.