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
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
= 3 + 4i changes the complexity of
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
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
Functions that sort complex values by absolute value include
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
real in MATLAB, but complex with zero-valued imaginary parts
in the generated code:
For MEX functions created by MATLAB Coder™:
Suppose that you generate the MEX function for complex inputs. If you call the MEX function with real inputs, the MEX function transforms the real inputs to complex values with zero-valued imaginary parts.
If the MEX function returns complex values that have all zero-valued imaginary parts, the MEX function returns the values to the MATLAB workspace as real values. For example, consider this function:
function y = foo() y = 1 + 0i; % y is complex with imaginary part equal to zero end
If you generate a MEX function for
view the code generation report, you see that
codegen foo -report
If you run the MEX function, you see that in the MATLAB workspace,
the result of
foo_mex is the real value
z = foo_mex
ans = 1
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
+ 3i and
y has the value
3i. In MATLAB, this code produces the real result
= 4. During code generation, the types for
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.
the complex result
4 + 0i in generated code, not
as in MATLAB code.
Exceptions to this behavior are:
When the imaginary parts of complex results are zero, MEX functions return the results to the MATLAB workspace as real values. See Inputs and Outputs for MEX Functions Generated for Complex Arguments.
When the imaginary part of the argument is zero, complex arguments to extrinsic functions are real .
function y = foo() coder.extrinsic('sqrt') x = 1 + 0i; % x is complex y = sqrt(x); % x is real, y is real end
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.