Cannot compile MEX LAPACK example - matlab

Question

Summary
I am trying to write some MEX files that use LAPACK, and I thought I'd start by looking through the examples provided by MathWorks.
However, I am having some trouble compiling them. After copying the matrixDivide.c example from [MATLAB root]/extern/examples/refbook into a working directory, I tried to build a mex file, but it failed with error undefined reference to `dgesv_' (where dgesv is the name of the LAPACK routine being called).
I was able to build a different mex example (timestwo.c) that doesn't use LAPACK.
So what's going on? What's the deal with the trailing underscore? What about this memcpy warning?
More info
I think this is fairly similar to the issues encountered by this user:
How can I use CLAPACK,BLAS or LAPACK in a mex file?
I've tried this with MATLAB R2013b and R2014b. I am running on 64-bit Linux (RHEL 6) and my compiler is gcc 4.4.7 (which is not the MathWorks recommended version, but is the newest version I can get).
Here are the relevant portions of the code I'm trying to compile:
1 /*=========================================================
2 * matrixDivide.c - Example for illustrating how to use
3 * LAPACK within a C MEX-file.
4 *
5 * X = matrixDivide(A,B) computes the solution to a
6 * system of linear equations A * X = B
7 * using LAPACK routine DGESV, where
8 * A is an N-by-N matrix
9 * X and B are N-by-1 matrices.
10 *
11 * This is a MEX-file for MATLAB.
12 * Copyright 2009-2010 The MathWorks, Inc.
13 *=======================================================*/
14 /* $Revision: 1.1.6.3 $ $Date: 2011/01/28 18:11:56 $ */
15
16 #if !defined(_WIN32)
17 #define dgesv dgesv_
18 #endif
19
20 #include "mex.h"
21 #include "lapack.h"
22
23 void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
24 {
[ snip ]
73 /* Call LAPACK */
74 dgesv(&m,&n,A2,&m,iPivot,B2,&p,&info);
75 /* plhs[0] now holds X */
76
77 mxDestroyArray(Awork);
78 mxDestroyArray(mxPivot);
79 }
Here is the output of the failed mex build:
>> mex -v -largeArrayDims matrixDivide.c
-> mexopts.sh sourced from directory (DIR = $MATLAB/bin)
FILE = /sw/matlab/R2013b/bin/mexopts.sh
----------------------------------------------------------------
-> MATLAB = /sw/matlab/R2013b
-> CC = gcc
-> CC flags:
CFLAGS = -ansi -D_GNU_SOURCE -fexceptions -fPIC -fno-omit-frame-pointer -pthread
CDEBUGFLAGS = -g
COPTIMFLAGS = -O -DNDEBUG
CLIBS = -Wl,-rpath-link,/sw/matlab/R2013b/bin/glnxa64 -L/sw/matlab/R2013b/bin/glnxa64 -lmx -lmex -lmat -lm -lstdc++
arguments =
-> CXX = g++
-> CXX flags:
CXXFLAGS = -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread
CXXDEBUGFLAGS = -g
CXXOPTIMFLAGS = -O -DNDEBUG
CXXLIBS = -Wl,-rpath-link,/sw/matlab/R2013b/bin/glnxa64 -L/sw/matlab/R2013b/bin/glnxa64 -lmx -lmex -lmat -lm
arguments =
-> FC = gfortran
-> FC flags:
FFLAGS = -fexceptions -fbackslash -fPIC -fno-omit-frame-pointer
FDEBUGFLAGS = -g
FOPTIMFLAGS = -O
FLIBS = -Wl,-rpath-link,/sw/matlab/R2013b/bin/glnxa64 -L/sw/matlab/R2013b/bin/glnxa64 -lmx -lmex -lmat -lm
arguments =
-> LD = gcc
-> Link flags:
LDFLAGS = -pthread -shared -Wl,--version-script,/sw/matlab/R2013b/extern/lib/glnxa64/mexFunction.map -Wl,--no-undefined
LDDEBUGFLAGS = -g
LDOPTIMFLAGS = -O
LDEXTENSION = .mexa64
arguments =
-> LDCXX =
-> Link flags:
LDCXXFLAGS =
LDCXXDEBUGFLAGS =
LDCXXOPTIMFLAGS =
LDCXXEXTENSION =
arguments =
----------------------------------------------------------------
-> gcc -c -I/sw/matlab/R2013b/extern/include -I/sw/matlab/R2013b/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fexceptions -fPIC -fno-omit-frame-pointer -pthread -O -DNDEBUG "matrixDivide.c"
In file included from matrixDivide.c:21:
/sw/matlab/R2013b/extern/include/lapack.h:6907:1: warning: "dgesv" redefined
matrixDivide.c:17:1: warning: this is the location of the previous definition
matrixDivide.c: In function `mexFunction':
matrixDivide.c:64: warning: incompatible implicit declaration of built-in function ?memcpy?
-> gcc -O -pthread -shared -Wl,--version-script,/sw/matlab/R2013b/extern/lib/glnxa64/mexFunction.map -Wl,--no-undefined -o "matrixDivide.mexa64" matrixDivide.o -Wl,-rpath-link,/sw/matlab/R2013b/bin/glnxa64 -L/sw/matlab/R2013b/bin/glnxa64 -lmx -lmex -lmat -lm -lstdc++
matrixDivide.o: In function `mexFunction':
matrixDivide.c:(.text+0x1c6): undefined reference to `dgesv_'
collect2: ld returned 1 exit status
mex: link of ' "matrixDivide.mexa64"' failed.

Answer 1

After some more messing around, I figured out my (rather elementary) mistake.
You need to specify the -lmwlapack option (and/or -lmwblas, as appropriate) to the linker:
mex -largeArrayDims -lmwlapack matrixDivide.c
It even says so on the MathWorks page I was trying to follow along on. RTFM!