Following True or False?

Consider the following example. a and b are two random variables. The loop will exit if and only if a+b=1. Is it true or false?

      a=rand;
      b=rand;
      while(a+b == 1)
          a=rand;
          b=rand;
      end

[Sabarinathan Vadivelu]

I found that sometimes the sum was exceeding 1 or less than 1. Why?

Answer 1

[Walter Roberson]

While executes as long as the given condition is true, so the loop would only execute as long as the sum was 1.

Note: please take time to review the following: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[Sabarinathan Vadivelu]

But sir, I found that when adding both values I'm getting a value greater than 1.

a=0.7849 and b=0.9728. this value I got one time.

[Walter Roberson]

If the sum was greater than 1, then a+b == 1 would be false, so your loop as written would not execute, so the values would be left unchanged.

[Sabarinathan Vadivelu]

How can I overcome this problem? How to satisfy that condition? It should be a +b = 1. No other values should come.

[Jan]

If a+b must be 1, simply use:

a = rand;  b = 1 - a;

It is extremely unlikely that two random numbers will have a sum of 1. I think the probability is in the magnitude of 10^-53. Therefore rejecting the values until the sum equals 1 will take a looong time.

[Walter Roberson]

      a=rand;
      b=rand;
      while(a+b ~= 1)
          a=rand;
          b=rand;
      end