That while will be asked to process the result of
any(~(abs(changeinvoltage_load)<=0.00001)) && any(~(abs(changeinvoltage_pv)<=0.00001)) && iter > 1 && iter <100
That is a series of conditions separated with && . In order to use && each of the conditions must evaluate to a scalar.
any(~(abs(changeinvoltage_load)<=0.00001))
will evaluate to a scalar provided that ~(abs(changeinvoltage_load)<=0.00001) evaluates to a scalar or to a vector. The code would have a problem if changeinvoltage_load were a 2D array. With a vector, each of the individual logical values (abs(changeinvoltage_load)<=0.00001) would be calculated, each of them would be logically negated because of the ~, and then any() would return true if at least one of those values were true. An equivalent expression would be
any( abs(changeinvoltage_load) > 0.00001 )
The second sub-expression any(~(abs(changeinvoltage_pv)<=0.00001)) follows the same logic.
The third subexpression iter > 1 is scalar true provided that iter is larger than 1. If iter is less than or equal to 1 at the start then the condition would be false and that would make the overall && false, leading to the while loop body never being executed. You initialize iter = 0, so the body of the while loop is never executed.
The fourth subexpression iter < 100 is scalar true provided that iter is less than 100. If iter is 0 or 1 at the beginning then the condition would not be reached because the previous condition would have been false.
There is probably no good reason for having the iter > 1 test in the while unless you want to be able to disable the while loop.
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