MATLAB: MATLAB C++ Complex Numbers

ccomplex numbersMATLAB

I have a MATLAB function that calculates wave phases using a -j in a multiplication statement. When I compile this into a C++ shared library I get an error that complex integer arithmetic is not supported. I tried substituting complex(0,-1) for -j, but that results in the same error.

Is there any workaround for this?

EDIT: It's MATLAB 7.11.0(R2010b) I'm running it on Windows XP (32 bit.)

I'm able to compile the matlab code into a C++ shared library. The matlab code doesn't do any I/O operations – that is all handled by the c++ natively and then passed into the matlab functions. The compiled library will throw an exception when it hits the complex arithmetic. Using the mclGetLastErrorMessage function I see that the error is "Error using ==> times Complex integer arithmetic is not supported." and then a pointer to the line of the MATLAB file where I use -j.

Best Answer

Is your c++ code passing integer or double complex data as an input to the compiled code?

MATLAB can not do complex math on integer types. Test your code from MATLAB exactly the way it will be used before compiling:

>> a=int32(1+i);
>> a*3
Error using  .* 
Complex integer arithmetic is not supported.
>> b=1+i;
>> b*int32(5)
Error using  .* 
Complex integer arithmetic is not supported.

Related Solutions

MATLAB: Is there a way to do signed 16 bit integer math

"... In standard C programming ..."

Well, sort of. Signed integer overflow behavior is not really defined in the C language. It is left up to the compiler to determine what happens for a particular implementation. Also there is the fact that binary operations in C (such as minus) with integers shorter than an int will first be converted to int to do the calculation (even if the shorter integer is unsigned). So your calculation above is actually done as follows assuming e.g. short is 16-bit and int is 32-bit:

signed short a=32558, b=-32333, c;
c = (signed short)( (int)b - (int)a );

So the subtraction is done with int's and there is no overflow for the result at the int level using the values you have above. The overflow actually occurs on the assignment, and that is where the particular compiler rules for this behavior come into play.

Now as it turns out, most platforms these days use 2's complement for integer representation and the C compilers choose to handle signed integer overflow by silently maintaining the same bit pattern of the operation result in a modulo sense, but this is not a requirement and it is not mandated that things work this way.

MATLAB truncates integer overflow operations, so yes there will be a mismatch. To get the same behavior at the MATLAB level, you would first need to convert all operands to single or double, do the operation, then modulo the result with an appropriate value depending on the bitsize of the intended target (int8 or int16 etc), and finally store that result in the integer variable. E.g.,

c = int16(mod(double(b)-double(a),32768));

MATLAB: Are C++ shared library targets supported with MATLAB Compiler 3.0 (R13)

This has been verified as an error within the documentation for the MATLAB Compiler within the section for MCC. C++ shared library targets are not supported with MATLAB Compiler 3.0 (R13).

Best Answer

Related Solutions

MATLAB: Is there a way to do signed 16 bit integer math

MATLAB: Are C++ shared library targets supported with MATLAB Compiler 3.0 (R13)

Related Question