Why use "+=" rather than "+" to change delta value of customer property

zhou zilong

Dear guys

I have a question about getDelta when using getDelta() in the API. When I follow the "EDEM API Tutorial 5 - Relative Wear"  and "Tutorial 7 - HM with Pressure Calculation", the doucment told me if I want to change the value of customer property I should assign the Delta a value.  Then Delta is added to the Custom Property Value at the end of the time-step. But I don't understand why use "+=" rather than "=" to assign the Delta value. When use "+=", the New Delta is the sum of the current Delta and the historical Delta instead of the current Delta. Then the New Property Value = History Property Value + Current Delta +Historical Delta rather than New Property Value = History Property Value + Current Delta  . I feel confussed. Please help me!

Best wishes

Zhou

Stephen Cole

Hi Zhou,

With Custom Properties it is always Value(t+1) = Value(t) + Delta(t) 

Regardless of how it is summed the Value at the next time-step is always the result of the current value + the resultant Delta.

For Operators this is a useful link - https://cplusplus.com/doc/tutorial/operators/

The confusion potentially comes in that the Delta(t) can come from different sources, you can add a delta from a Body Force as well as a Contact Model, or from multiple sources inside 1 model.  

It's up to how you write the code if you want to use += or = but this only affects the resultant Delta at time t, it doesn't influence how the calculation for the final Value is done.  For example:

//code delta[0] += 10.0; //more code delta[0] = 1.0;

In the above the resultant Delta would be 1.0 as the second time we add to the delta we are overwriting any previous additions.  However with:

//code delta[0] += 10.0; //more code delta[0] += 1.0;

We're adding 11 to the Value at this time-step.

I hope this helps.

Regards

Stephen