SHELLG Loop Index Fix

[xawpaw]

If the loop variable N ever exceeds 100, it will result in an out-of-bounds error for the array P which is dimensioned as P(8,100).

To improve the code and ensure it does not run into array bounds issues, you can add a check within the loop to exit if N exceeds the upper bound of the array:

  SUBROUTINE SHELLG(LAT, LON, HEIGHT, DIMO, XL, ICODE, BAB1)
        REAL LAT, LON, HEIGHT, DIMO, XL, BAB1
        INTEGER ICODE
        REAL P(8,100)
        INTEGER N
        REAL STEP12

        ! Initialize STEP12 (Assuming it's calculated or assigned earlier in the code)
        STEP12 = ...

        ! Main loop with added bounds check
        DO 3 N = 3, 3333
            ! Exit the loop if N exceeds the bounds of P array
            IF (N > 100) THEN
                PRINT *, 'Warning: Loop variable N exceeds the bounds of array P. Exiting loop.'
                EXIT
            END IF

            ! Corrector (field line tracing)
            P(1, N) = P(1, N-1) + STEP12 * (5. * P(4, N) + 8. * P(4, N-1) - P(4, N-2))
            P(2, N) = P(2, N-1) + STEP12 * (5. * P(5, N) + 8. * P(5, N-1) - P(5, N-2))
            
            ! (Include other operations as necessary)
            
            CONTINUE
        END DO 3
    END SUBROUTINE SHELLG

This ensures that the array bounds are respected, preventing potential runtime errors or undefined behavior due to accessing out-of-bounds array elements. If the logic of the code ensures that the loop variable N never exceeds 100, this check will never trigger.

However, it's good practice to include such safeguards, especially in scientific and engineering code, where array bounds issues can lead to significant problems.

Mad Max