For code generation, you must set the complexity of variables at the time of
assignment. Assign a complex constant to the variable or use the `complex`

function. For
example:

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

After assignment, you cannot change the complexity of a variable. Code
generation for the following function fails because ```
x(k) = 3 +
4i
```

changes the complexity of `x`

.

function x = test1( ) x = zeros(3,3); % x is real for k = 1:numel(x) x(k) = 3 + 4i; end end

To resolve this issue, assign a complex constant to
`x`

.

function x = test1( ) x = zeros(3,3)+ 0i; %x is complex for k = 1:numel(x) x(k) = 3 + 4i; end end

For code generation, complex data that has all zero-valued imaginary parts remains complex. This data does not become real. This behavior has the following implications:

In some cases, results from functions that sort complex data by absolute value can differ from the MATLAB

^{®}results. See Functions That Sort Complex Values by Absolute Value.For functions that require that complex inputs are sorted by absolute value, complex inputs with zero-valued imaginary parts must be sorted by absolute value. These functions include

`ismember`

,`union`

,`intersect`

,`setdiff`

, and`setxor`

.

Functions that sort complex values by absolute value include
`sort`

, `issorted`

,
`sortrows`

, `median`

,
`min`

, and `max`

. These functions sort
complex numbers by absolute value even when the imaginary parts are zero. In
general, sorting the absolute values produces a different result than sorting
the real parts. Therefore, when inputs to these functions are complex with
zero-valued imaginary parts in generated code, but real in MATLAB, the generated code can produce different results than MATLAB. In the following examples, the input to `sort`

is real in MATLAB, but complex with zero-valued imaginary parts in the generated code:

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 line of code:

z = x + y;

Suppose that at run time, `x`

has the value ```
2 +
3i
```

and `y`

has the value ```
2 -
3i
```

. In MATLAB, this code produces the real result `z = 4`

.
During code generation, the types for `x`

and
`y`

are known, but their values are not known. Because
either or both operands in this expression are complex, `z`

is
defined as a complex variable requiring storage for 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.

When an operand of a complex multiplication contains a nonfinite value, the generated code might produce a different result than the result that MATLAB produces. The difference is due to the way that code generation defines complex multiplication. For code generation:

Multiplication of a complex value by a complex value (

*a*+*b*i) (*c*+*d*i) is defined as (*a**c*-*b**d*) + (*a**d*+*b**c*)i. The complete calculation is performed, even when a real or an imaginary part is zero.Multiplication of a real value by a complex value

*c*(*a*+*b*i) is defined as*c**a*+*c**b*i .