Controlling Flow

The if statement is a decision-making statement. In its simplest form, it looks like this:

if (x > 0)
  zz = 1/x;
end

The expression “x > 0” controls what the rest of the statement will do. The command “zz = 1/x” is executed only if the condition “x > 0” is true.

if (x > 0)
  zz = 1/x;
else
  zz = -1;
end

Comparing two numeric values uses one of the following relational operators. All of comparison operators return a value of 1 if the comparison is true, or 0 if it is false.

Further branches. When more than two branches are necessary, "elseif" can be used.

if (i - j == 0)
  B(i,j) = 1;
elseif (i - j == 1)
  B(i,j) = -1;
else
  B(i,j) = 0;
end

The for statement makes it convenient to execute a routine repeatly while counting iterations of a loop. It looks like this:

for i = 1:5
  x(i) = i^2;
end

The above code works by first evaluating the expression 1:5 to produce a range of values from 1 to 5. Then the variable i is assigned the first element of the range and

x(i) = i^2;

in the loop is executed once. And this process continues until there are no more elements to assign for i.

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