You could get a Decompiler that created C code. However, there is no known program for automatically converting C into MATLAB, and doing so is not generally possible as there are some things that can be done in C that cannot be done in MATLAB.
When MATLAB code is compiled to a .dll using MATLAB Compiler (in older versions) or MATLAB Compiler SDK (newer versions) then it is not compiled directly to C: instead, the internal threaded interpreted data structures are written as data in encrypted form, and a MATLAB runtime library is used to interpret the data structures at execution time. It is intended that this be difficult to convert back to MATLAB code.
