The function shifts each character in the input string forward by a certain number of positions in the alphabet based on the position of the character in the alphabet. The shift pattern is as follows: 20, 7, 23, 24, 14, 15, 5, 16, 11, 10, 18, 19, 9, 8, 6, 1, 4, 0, 3, 21, 12, 2, 13, 17, 22, 25.

[CODE]:
```python
def shift_function(input_string):
    shift_pattern = [20, 7, 23, 24, 14, 15, 5, 16, 11, 10, 18, 19, 9, 8, 6, 1, 4, 0, 3, 21, 12, 2, 13, 17, 22, 25]
    output_string = ""

    for char in input_string:
        position = ord(char) - ord('a')
        shift = shift_pattern[position]
        shifted_char = chr((ord(char) - ord('a') + shift) % 26 + ord('a'))
        output_string += shifted_char

    return output_string
```

This code should approximate the behavior of the function.