I never have problems using cvx, until I tried to use it on a university cluster. I get this error every time \begin{verbatim} Undefined function ‘cvx_begin’ for input arguments of type ‘char’.\end{verbatim}

If I need to provide more information please don’t hesitate. Thank you

I’m sorry, there’s just no way I’m going to be able to diagnose this from afar. I remain convinced it is simply not being set up properly on the cluster. You will have to do the setup yourself.

That’s an example of CVX producing misleading error messages. I think the design of CVX ensures (except for a few bugs) that an error message is generated if CVX’s rules are not followed. But sometimes the actual error message generated seemingly has nothing to do with the rule that was actually violated, or at least is non-informative as to what the true error is. The CVX developer is aware of this behavior, and could probably improve it if enough development effort were put in.

Well, I tried it out.

>> cvx_begin;variable x;x<=0<=1;cvx_end
Undefined function 'bcompress' for input arguments of type 'double'.
Error in cvxprob/newcnstr (line 233)
[ zR, zL ] = bcompress( z, cmode );
Error in <= (line 21)
b = newcnstr( evalin( 'caller', 'cvx_problem', '[]' ), x, y, '<=' );
>> cvx_clear;cvx_begin;variable x;0<=x<=1;cvx_end
Calling SDPT3 4.0: 2 variables, 1 equality constraints
------------------------------------------------------------
num. of constraints = 1
dim. of linear var = 2
*******************************************************************
SDPT3: Infeasible path-following algorithms
*******************************************************************
version predcorr gam expon scale_data
NT 1 0.000 1 0
it pstep dstep pinfeas dinfeas gap prim-obj dual-obj cputime
-------------------------------------------------------------------
0|0.000|0.000|9.5e+00|1.4e+01|2.0e+02| 0.000000e+00 0.000000e+00| 0:0:00| chol 1 1
1|1.000|1.000|3.3e-06|1.0e-01|9.0e+00| 0.000000e+00 -8.955355e+00| 0:0:00| chol 1 1
2|1.000|0.989|6.1e-08|1.1e-02|9.8e-02| 0.000000e+00 -9.061411e-02| 0:0:00| chol 1 1
3|1.000|0.989|1.9e-08|1.1e-03|1.1e-03| 0.000000e+00 -2.963690e-04| 0:0:00| chol 1 1
4|1.000|0.989|2.3e-09|1.1e-04|1.2e-05| 0.000000e+00 6.667558e-05| 0:0:00| chol 1 1
5|1.000|0.989|2.1e-10|1.2e-06|1.3e-07| 0.000000e+00 7.325592e-07| 0:0:00| chol 1 1
6|1.000|1.000|1.1e-12|4.2e-11|1.5e-09| 0.000000e+00 -1.438312e-09| 0:0:00|
stop: max(relative gap, infeasibilities) < 1.49e-08
-------------------------------------------------------------------
number of iterations = 6
primal objective value = 0.00000000e+00
dual objective value = -1.43831202e-09
gap := trace(XZ) = 1.47e-09
relative gap = 1.47e-09
actual relative gap = 1.44e-09
rel. primal infeas (scaled problem) = 1.15e-12
rel. dual " " " = 4.19e-11
rel. primal infeas (unscaled problem) = 0.00e+00
rel. dual " " " = 0.00e+00
norm(X), norm(y), norm(Z) = 7.1e-01, 1.4e-09, 2.1e-09
norm(A), norm(b), norm(C) = 2.4e+00, 2.0e+00, 1.0e+00
Total CPU time (secs) = 0.04
CPU time per iteration = 0.01
termination code = 0
DIMACS: 1.1e-12 0.0e+00 4.2e-11 0.0e+00 1.4e-09 1.5e-09
-------------------------------------------------------------------
------------------------------------------------------------
Status: Solved
Optimal value (cvx_optval): +0