error LNK2019: unresolved external symbol although included

I have a problem with using mex. When I use the command

mex mexT1Mapping.c

I get this error

Error using mex
   Creating library mexUtils.lib and object mexUtils.exp
mexT1Mapping.obj : error LNK2019: unresolved external symbol maxAbsArray referenced in function threadFunc

and this although I included in the mexT1Mapping.c function the function mexUtils.h with

#include "mexUtils.h";
So _maxAbsArray_ is included but mex does not find it. How can I solve it?
which has following code:

#ifndef MEXUTILS_H
#define MEXUTILS_H

int    signDouble (double x);
int    by_size    (const void * a, const void * b);
double maxAbsArray(double *x, int n);
double minAbsArray(double *x, int n);
double l2Array    (double *x, double *y, int n);
double mean       (double *x, int n);
double covar      (double *x, double *y, int n);
double corrcoef   (double *x, double *y, int n);
double mins        (double a, double b);
double maxs        (double a, double b);

#endif