Update RDoC_pt2.Rmd

- During the factor assignment phase of the validation process, the initial code erroneously considered non-absolute values when determining the greatest product sums between each map and the factors. We have corrected this error; because the number of high negative coefficients was relatively small, the results remained unchanged. 
- For the internal validation step, all 4 models (DD, DD (bifactor), RDoC, RDoC (bifactor)) are compared instead of only 2 before (DD (bifactor), RDoC).

Author: ShaunQuah