if:

	1) Introduction ------------------------------------------------

	The if statement is very similar to the C if statement. 

		if ( test-expression )
		{
		  statement(s)
		else
		  statement(s)
		}

	The "else" is optional, and the braces are always required.
	The differences between the C-language if-statement and RLaB's
	are due to the special demands of an interactive language.

	Examples:

		//-----------------------------------

		if ( init ) 
	        {
		  mass = 10.0;
		  inertia = 3*mass/length^3;
		  init = 0;
		}

		//-----------------------------------

		if(class(data) == "string") 
		{
		  fprintf(file, data);
		else
		  write(file, data);
		}

		//-----------------------------------

		if( class(v) != "matrix" ) { error(); }

		//-----------------------------------

	At present there is no explicit elseif statement. However the
	else if behavior can be implemented as it is in C (although
	RLaB's syntax is clumsier). For example:

		if( test1 ) 
		{
		  x = a;
		else if( test2 ) {
		  x = b;
		else if( test3 ) {
		  x = c;
		else 
		  error();
		}}}

	2) Finer Points  -----------------------------------------------

	The if statement requires that the test-expression be a scalar
	quantity. If it is necessary to test a matrix, the result of
	the matrix test must be reduced to a scalar quantity. The
	any(), all() and find() functions are useful in this
	situation.

	Example:

		> a = [1,2,3;4,5,6;7,8,9];
		> a < 100
		        1          1          1  
		        1          1          1  
		        1          1          1  
		> all (a < 100)
		        1          1          1  
		> all (all (a < 100))
		        1  

	In the above example, the result of a matrix test was first
	reduced to a vector result with one use of all(). A second use
	of all() reduces the vector result to a scalar result, which
	is now suitable for inclusion in an if statement
	test-expression.

		> if (all (all (a < 100))) { "all a < 100" }
		all a < 100

