Urgent! UDF error "implicit declaration of function"
Urgent, will wait online for answers!
After compiling the following UDF, I see the error message "inlet_u.c:39: warning: implicit declaration of function erf". And the simulation crash if I continue using this UDF. The only problem is the function erf. But I have included math.h, anything else needs to be done? Or math.h is NOT the right header file to include if I want to use function erf? erf is error function. What is the reason? and How can I solve it? Thanks! /* UDF for specifying a transient inlet velocity profile boundary condition */ #include "udf.h" #include "math.h" #define PI 4.*atan(1.) #define RT 0.00183 real VM=21.911; real VNin=0.01; /**************** x velocity ****************/ DEFINE_PROFILE(v_x, thread, index) { face_t f; real t,dt,u; real D1,D2,D3,D4,D5,D6,D7; real G1,G2,G3; /* wind gust model parameters */ D1=VM*700; D2=7/(3*RT); D3=1; D4=3/(3*RT); D5=0.15; D6=7/(10*RT); D7=2*PI/(RT/10); /* get flow time */ t = CURRENT_TIME; /* u = X Velocity */ if (t<=VNin*RT) { u = VM;} else { /* get dt */ dt = tVNin*RT; /* wind gust model */ G1=D1*dt*exp(D2*dt); G2=D3*erf(D4*dt); G3=D5*exp(D6*dt)*sin(D7*dt); /* get u */ u = VM+G1+G2+G3;} /* assign X velocity */ begin_f_loop(f, thread) { F_PROFILE(f, thread, index) = u; } end_f_loop(f, thread) } 
I suppose you are on a Windows system ? If yes the erf function is not implemented in math.h . So basically you will need to implement a custom version of erf in your UDF function.
If you are on Linux erf should be already defined in math.h so you need to search for the error in a different place. Do 
(post here again to make sure you can see my response)
Thank you so much for replying. I run Fluent on Linux. I searched the src folder (it contains the udf.h file) for the file math.h and did NOT find it. If I have to implement a custom version of erf, how to do it? I checked the UDF manual, it says "C compilers include a library of standard mathematical and I/O functions", but it does not say what if I want to use a function like erf. 
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