Why is the following UDF not being compiled as an interpreted UDF?

#include "udf.h" DEFINE_PROPERTY(cell_temperature,cell,thread) {

real temp = C_T(cell,thread);

face_t f;

real flow_time = RP_Get_Real("flow-time");

begin_f_loop (f,thread)

{

if (flow_time = 0)

temp = 300;

else

temp = 350;

return temp;

}

Error is:line 12: invalid expression for if : float

This error comes from unability to check equality between integer and real numbers. You could change the line

if (flow_time = 0) to if (flow_time < 1.0e-7)

and this line should be OK. I don't have much experience with UDF, but i'm not sure with what you are trying to achieve with this one. Temperature is not property, why dont't you use DEFINE_PROFILE or a field function?

Hope it helps

Note that the equality operator in C is ==.

You have an assignment (setting flow_time to zero), not an equality test.

Dear kostya, thanks for the comments. But really I am still confused about the UDF to be used. Actually I want to define an energy source from time t=0 secs to time t=60 secs (i.e. 1 minute) at the constant value of say 5 W/m3. Then I want to stop the energy source ( at t > 60 secs), and find out the temperature profile as a function of temperature and time. Following is the crude form of the program, which of course has errors, as they appear on the console window.

#include "udf.h" DEFINE_SOURCE(energy_source,cell,thread,dS,eqn) {

real source;

real flow_time = RP_Get_Real("flow-time");

{

if (flow_time < 1.0e-7)

source = 0.;

for (flow_time>=1.0e-7; flow_time<=60;

source = 5.0;

else

source = 0.;

dS[eqn] = 0.0;

return source;

}

The compilation errors that appear are as follows:

Error: source.cpp: line 10: parse error. Error: source.cpp: line 11: parse error. Error: source.cpp: line 17: parse error.

Here source.cpp is the relevant file.

Another question that I would like to ask is about the error. What is the meaning of parse error?

I've just started to learn to program in C and use these UDF's also. I found a parse error just to mean a format error of some type (ie the use of brackets inside your 'if' loops, if you have more than 1 line after your 'if' and 'else' statements you need to put the '{' brackets in)

cheers,

Matthew.

A parse error indicates that the code is not syntactically valid C. You are going to need to learn C to do anything effective with UDFs. Here is a version of your code that sets source to 5 if flow-time is between (0,60] and 0 otherwise. I am not familiar with the DEFINE_SOURCE hook so I can't comment on whether it is doing something useful.

#include "udf.h"

DEFINE_SOURCE(energy_source,cell,thread,dS,eqn) {

real source;

real flow_time = RP_Get_Real("flow-time");

if (flow_time > 0.0 && flow_time <= 60.)

source = 5.0;

else

source = 0.0;

dS[eqn] = 0.0;

return source;

}