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Help on WHILE from MATLAB
The following MATERIAL is copied DIRECTLY from MATLAB is completely
the property of MATHWORKS. I have given links to where you will find
the following help.
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>> help while

WHILE  Repeat statements an indefinite number of times.
    The general form of a WHILE statement is:
  
       WHILE expression
         statements
       END
  
    The statements are executed while the real part of the expression
    has all non-zero elements. The expression is usually the result of
    expr rop expr where rop is ==, <, >, <=, >=, or ~=.
 
    The BREAK statement can be used to terminate the loop prematurely.
 
    For example (assuming A already defined):
  
            E = 0*A; F = E + eye(size(E)); N = 1;
            while norm(E+F-E,1) > 0,
               E = E + F;
               F = A*F/N;
               N = N + 1;
            end
 
    See also FOR, IF, SWITCH, BREAK, END.
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From MATLAB->Getting Started->Programming with MATLAB->while

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.
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From MATLAB->Using MATLAB->M-File Programming->
Programming and Data Types: M-File Programming: while

The while loop executes a statement or group of statements repeatedly
as long as the controlling expression is true (1).

Its syntax is

    while expression
	  statements
    end

If the expression evaluates to a matrix, all its elements must be 1
for execution to continue. To reduce a matrix to a scalar value, use
the all and any functions.

For example, this while loop finds the first integer n for which n! (n
factorial) is a 100-digit number.

	   n = 1;
           while prod(1:n) < 1e100
		 n = n + 1;
	   end

Exit a while loop at any time using the break statement.

while Statements and Empty Arrays
A while condition that reduces to an empty array represents a false
condition. That is,

	   while A, S1, end

never executes statement S1 when A is an empty array.
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From MATLAB Function Reference: while

WHILE
Repeat statements an indefinite number of times

Syntax
while expression
    statements 
end

Description
while repeats statements an indefinite number of times. The statements
are executed while the real part of expression has all nonzero
elements. 

expression is usually of the form

	   expression rop expression

where rop is ==, <, >, <=, >=, or ~=.

The scope of a while statement is always terminated with a matching end.

Examples
The variable eps is a tolerance used to determine such things as near
singularity and rank. Its initial value is the machine 
epsilon, the distance from 1.0 to the next largest floating-point
number on your machine. Its calculation demonstrates while loops:

       eps = 1;
       while (1+eps) > 1
           eps = eps/2;
       end
       eps = eps*2

See Also
all, any, break, end, for, if, return, switch
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