Getting Started

while

The while loop repeats a group of statements an indefinite number of times under control of a logical condition. A matching end delineates the statements.

Here is a complete program, illustrating while, if, else, and end, that uses interval bisection to find a zero of a polynomial.

• a = 0; fa = -Inf;
  b = 3; fb = Inf;
  while b-a > eps*b
     x = (a+b)/2;
     fx = x^3-2*x-5;
     if sign(fx) == sign(fa)
        a = x; fa = fx;
     else
        b = x; fb = fx;
     end
  end
  x
  

The result is a root of the polynomial x³ - 2x - 5, namely

• x =
     2.09455148154233
  

The cautions involving matrix comparisons that are discussed in the section on the if statement also apply to the while statement.

for

continue