Upgrade MEX Files to Interleaved Complex API

Convert C, C++, and Fortran MEX source files from the Separate Complex (SC) API to the Interleaved Complex (IC) API, following the MathWorks upgrade workflow with guardrails for SC/IC guarded builds using MX_HAS_INTERLEAVED_COMPLEX, required vs recommended changes, and verification.

When to Use

• User has a C, C++, or Fortran MEX file using mxGetPr/mxGetPi, mxGetData/mxGetImagData, or mxSetPr/mxSetPi
• User wants to build with mex -R2018a
• User asks about interleaved complex, IC MEX, or modernizing MEX code
• User has legacy MEX code from File Exchange, GitHub, or pre-R2018a era
• User has a C++ MEX file (.cpp, .cxx) using the C Matrix API (mxGetPr/mxGetPi, etc.)
• User has a Fortran MEX file (.F, .f90) using mxGetPr/mxGetPi via %val() pointers
• User reports a MEX function is slow on large complex arrays (call overhead, not loop)
• User asks how to improve MEX performance for complex data

When NOT to Use