compilation error in nlopt\src\algs\neldermead\nldrmd.c (beta redefined)

[p-j-miller]

What happened?

The issue is that some systems define beta in math.h and this causes a compilation error as there is a variable "beta" in the code.
The issue was found using C++ builder V12.1 on Windows which uses the clang compiler but a quick web search suggests the function double beta(double x, double y); was originally proposed in https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1292.pdf and is now present in a number of compiler header files.

How to reproduce the issue?

The actual problem is present on line 35 of nlopt\src\algs\neldermead\nldrmd.c :  

 static const double alpha = 1, beta = 0.5, gamm = 2, delta = 0.5;

The obvious fix is to rename beta (I used sbeta). This constant is only used in line 254 so that also needs to be changed:

  if (!reflectpt(n,xcur,c, fh <= fr ? -sbeta : sbeta, xh, lb,ub)) {

Version

2-10-0 (but I assume this is present in all versions of nlopt)

Operating System

unknown

Installation media

unknown

Additional Context

No response

[jschueller]

it doesn't seem present in other compilers, was this actually accepted into the standard ?
maybe you can get away with -Dbeta=sbeta compiler flag passed through CMAKE_C_FLAGS ?

[p-j-miller]

Thanks for the suggestion - however when I tried it I got the same error as the preprocessor changed both the definition in math.h and nldrmd.c . I could not find a way to avoid this using compiler flags. I use the Clang compiler. I have just checked and its possible to get the same issue with gcc - but probably not by default if I've interpreted its math.h header correctly.

[stevengj]

I'm fine with renaming these variables to ALPHA, BETA, GAMMA, and DELTA (better to do them all for consistency).

A PR would be welcome.

[marcoafo]

I've used this library a lot, so I'll try to contribute with that.

[stevengj]

Closed by #622