## Documentation Center |

On this page… |
---|

For code generation, you must set the complexity of variables
at the time of assignment, either by assigning a complex constant
or using the `complex` function,
as in these examples:

x = 5 + 6i; % x is a complex number by assignment. y = 7 + 8j; % y is a complex number by assignment. x = complex(5,6); % x is the complex number 5 + 6i.

Once you set the type and size of a variable, you cannot cast
it to another type or size. In the following example, the variable `x` is
defined as complex and stays complex:

x = 1 + 2i; % Defines x as a complex variable. y = int16(x); % Real and imaginary parts of y are int16. x = 3; % x now has the value 3 + 0i.

Mismatches can also occur when you assign a real operand the complex result of an operation:

z = 3; % Sets type of z to double (real) z = 3 + 2i; % ERROR: cannot recast z to complex

As a workaround, set the complexity of the operand to match the result of the operation:

m = complex(3); % Sets m to complex variable of value 3 + 0i m = 5 + 6.7i; % Assigns a complex result to a complex number

In general, expressions that contain one or more complex operands produce a complex result in generated code, even if the value of the result is zero. Consider the following example:

x = 2 + 3i; y = 2 - 3i; z = x + y; % z is 4 + 0i.

In MATLAB^{®}, this code generates the real result `z
= 4`. During code generation, the types for `x` and `y` are
known, but their values are not. Because either or both operands in
this expression are complex, `z` is defined as a
complex variable requiring storage for both a real and an imaginary
part. `z` equals the complex result `4 +
0i` in generated code, not `4` as in MATLAB code.

Exceptions to this behavior are:

Functions that take complex arguments but produce real results return real values.

y = real(x); % y is the real part of the complex number x. y = imag(x); % y is the real-valued imaginary part of x. y = isreal(x); % y is false (0) for a complex number x.

Functions that take real arguments but produce complex results return complex values.

z = complex(x,y); % z is a complex number for a real x and y.

Was this topic helpful?