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Old   September 20, 2011, 15:00
Default return in udf
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What is the main function of 'return' in udf? Since I had gone through the guide and I found that certain udf with 'return' while some did not. What the different of udf with 'return' and udf with no 'return'?
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Old   September 20, 2011, 15:07
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Originally Posted by wlt_1985 View Post
What is the main function of 'return' in udf? Since I had gone through the guide and I found that certain udf with 'return' while some did not. What the different of udf with 'return' and udf with no 'return'?
Dear Raymond,
if your macro is void-type, it wouldn't return any value and it just does some settings, but if it isn't void-type, it return a value and needs return command.

Bests,
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Old   September 21, 2011, 01:26
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Dear Raymond,
if your macro is void-type, it wouldn't return any value and it just does some settings, but if it isn't void-type, it return a value and needs return command.

Bests,
Thanks Amir. For example, I am having changes in species during the modelling, then I am either using macro DEFINE_SOURCE or DEFINE_VR_RATE. DEFINE_SOURCE does have 'return' while DEFINE_VR_RATE does not have. Does it mean that DEFINE_VR_RATE just doing some setting which has been pre-defined in Fluent while DEFINE_SOURCE calling for calculation and return the value to the model? Please help.
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Old   September 21, 2011, 02:16
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Hi,

Your reasoning is correct; In DEFINE_SOURCE, you return the value of the source directly (through the "return" command), while in DEFINE_VR_RATE you update the specific reaction rate pointer (*rr_t) which is predefined by FLUENT.

Cheers!
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Old   September 21, 2011, 02:26
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Originally Posted by wlt_1985 View Post
Thanks Amir. For example, I am having changes in species during the modelling, then I am either using macro DEFINE_SOURCE or DEFINE_VR_RATE. DEFINE_SOURCE does have 'return' while DEFINE_VR_RATE does not have. Does it mean that DEFINE_VR_RATE just doing some setting which has been pre-defined in Fluent while DEFINE_SOURCE calling for calculation and return the value to the model? Please help.
Exactly; in DEFINE_SOURCE, there isn't any argument which refers to source value, so we define a real variable, e.g. source, and use return function at the end;
Code:
return source
But in DEFINE_VR_RATE, there are two argument which are pre-defined for FLUENT and you can store desired data in them. It's defined for this macro which variable should be returned, so you wouldn't need return command.

Bests,
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Old   September 21, 2011, 04:35
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Originally Posted by Amir View Post
Exactly; in DEFINE_SOURCE, there isn't any argument which refers to source value, so we define a real variable, e.g. source, and use return function at the end;
Code:
return source
But in DEFINE_VR_RATE, there are two argument which are pre-defined for FLUENT and you can store desired data in them. It's defined for this macro which variable should be returned, so you wouldn't need return command.

Bests,
Thanks Amir.
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