To define a custom variable in a DFLUX subroutine in ABAQUS that can be updated and stored in memory each time the subroutine is executed, you can make use of the DFLUX array.

The DFLUX array is an output variable of the DFLUX subroutine that stores the flux values computed by the subroutine. By appropriately manipulating the DFLUX array, you can create and update your custom variable.

Here's an example of how you can define and update a custom variable inside a DFLUX subroutine:

Declare the custom variable: Declare your custom variable at the beginning of the DFLUX subroutine. For example:

DOUBLE PRECISION :: myVariable

Update the custom variable: Inside the DFLUX subroutine, update the value of your custom variable based on the desired calculations and conditions. For example:

myVariable = ... ! Update the custom variable based on calculations

Store the custom variable in DFLUX: Assign the value of your custom variable to the appropriate location in the DFLUX array. The DFLUX array has the same dimensions as the flux array and stores the computed flux values. Choose an appropriate location in the DFLUX array to store your custom variable. For example:

DFLUX(1,1) = myVariable ! Store the custom variable in DFLUX

Use the custom variable outside the DFLUX subroutine: Once the DFLUX subroutine is executed, you can access the updated value of your custom variable by examining the corresponding location in the DFLUX array. For example:

myUpdatedVariable = DFLUX(1,1) ! Access the updated custom variable stored in DFLUX

Remember to ensure that the dimensions and indexing of your custom variable in the DFLUX array align correctly with your specific implementation.

By following these steps, you can define and update a custom variable inside the DFLUX subroutine and store it in memory each time the subroutine is executed. You can then use the updated value of the custom variable outside the subroutine as needed.