MATLAB mex - Undefined symbols _max

Question

I'm trying to use the following C file in a MATLAB script using mex.

#include <math.h>
#include "mex.h"
#include "blas.c"



static void lbidiagQR (int n, double* gamma, double* delta, double mu,
                          double* Q, double* u, double* v)
{
int i, ldQ ;
double tmp ;

ldQ  = n*2 ;
u[0] = gamma[0] ;
for (i = 0 ; i < n ; ++i)
{
    tmp = mu ;
    rotg (&u[i], &tmp, &Q[i*2],   &Q[i*2  +ldQ]) ;

    tmp = delta[i] ;
    rotg (&u[i], &tmp, &Q[i*2+1], &Q[i*2+1+ldQ]) ;

    if (i < n-1)
    {
        v[i]   = 0.0 ;
        u[i+1] = gamma [i+1] ;

        rot (&v[i], &u[i+1], Q[i*2+1], Q[i*2+1+ldQ]) ;
    }
}
}

// input arguments
#define gamma prhs[0]
#define delta prhs[1]
#define mu    prhs[2]

// output arguments
#define Q     plhs[0]
#define u     plhs[1]
#define v     plhs[2]

void mexFunction (int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[])
{
int n ;

// check for proper number of arguments
if (nrhs != 3) mexErrMsgTxt ("lbidiagQR requires three input arguments.")  ; else
if (nlhs != 3) mexErrMsgTxt ("lbidiagQR requires three output arguments.") ;

// check the dimensions of gamma
n = max (mxGetM (gamma), mxGetN (gamma)) ;
if (min (mxGetM (gamma), mxGetN (gamma)) != 1)
    mexErrMsgTxt ("gamma must be an n-by-1 or a 1-by-n matrix.") ;

// check the dimensions of delta
if ((min (mxGetM (delta), mxGetN (delta)) != 1) ||
    (max (mxGetM (delta), mxGetN (delta)) != n))
    mexErrMsgTxt ("delta must be an n-by-1 or a 1-by-n matrix.") ;

// check the dimensions of mu
if ((mxGetM (mu) != 1) || (mxGetN (mu) != 1))
    mexErrMsgTxt ("mu must be a scalar.") ;

// create matrices for the return arguments
Q = mxCreateDoubleMatrix (n*2, 2, mxREAL) ;
u = mxCreateDoubleMatrix (n,   1, mxREAL) ;
v = mxCreateDoubleMatrix (n-1, 1, mxREAL) ;

// do the actual computations in a subroutine
lbidiagQR (n, mxGetPr (gamma), mxGetPr (delta), *mxGetPr (mu),
              mxGetPr (Q), mxGetPr (u), mxGetPr (v)) ;
}

However this trows the error:

c_routines/lbidiagqr.c:75:9: warning: implicit declaration of function 'max' is invalid in C99
  [-Wimplicit-function-declaration]
n = max (mxGetM (gamma), mxGetN (gamma)) ;
    ^
c_routines/lbidiagqr.c:76:9: warning: implicit declaration of function 'min' is invalid in C99
  [-Wimplicit-function-declaration]
if (min (mxGetM (gamma), mxGetN (gamma)) != 1)
    ^
2 warnings generated.
Undefined symbols for architecture x86_64:
"_max", referenced from:
  _mexFunction in lbidiagqr.o
"_min", referenced from:
  _mexFunction in lbidiagqr.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

mex: link of ' "lbidiagqr.mexmaci64"' failed.

Which seesm to me to suggest that the lines using max() and min() are the problem. Having looked around I see that these can be defined using a macro as:

#define max(a,b) \
({ __typeof__ (a) _a = (a); \
__typeof__ (b) _b = (b); \
_a > _b ? _a : _b; })

#define max(a,b) \
({ __typeof__ (a) _a = (a); \
__typeof__ (b) _b = (b); \
_a < _b ? _a : _b; })

Though this does not solve the error though I now get a warning about redefining the macros in the code. The linking error persists.

I am running (regrettably given the whole 'clang' debacle) OSX mavericks with MATLAB R2012b. And I would really appreciate any help on this.

Answer 1

I may have solved the problem.

Defining these as a macro has not worked, though in my case I can get away by assuming these values are floats (as they will be in the matlab code). With this knowledge I used the functions in math.h fmin() fmax()

This lets the code compile fine.

A little longer and I will be able to see completely if this has worked as the code will be fully run-able.

EDIT:

Yes! That solved the problem. Knowing explicitly that the values are floats allowed me to use fmin and fmax in place of min and max within the C code to compile, link and run successfully.

Sorry for using this space to rubber-duck debug but maybe this will be useful to someone in the future. Good luck with your problem future person.