I found this on if-elseif-else in the documentation of R14.
If the evaluated expression yields a nonscalar value, then every element of this value must be true or nonzero for the entire expression to be considered true. For example, the statement if (A < B) is true only if each element of matrix A is less than its corresponding element in matrix B.
Matlab may contain the old code even if is not documented. Backward compatibility for old-timers.
For every elseif expression the Code Analyzer reports
When both arguments are numeric scalars, consider replacing | with || for performance.
I take that as a hint that the old code is still there.
The the documentation of recent releases don't say anything about scalar or nonscalar expressions. It goes without saying that the values of the expressions are scalar. (As far as I can see.)
The call f([606:609]') reproduces the error you report.
Output argument "y" (and maybe others) not assigned during call to "f>f_".
Error in f (line 7)
y = f_([606:609]')
Your expressions, e.g. (T1+i*7+dstep<t), are noncalar when f() is called with a vector.
What Matlab release are you using?
How did you call f() ?