question about tract.js

[snake0327]

        var r = this.reflection[i] * (1-lambda) + this.newReflection[i]*lambda;
        var w = r * (this.R[i-1] + this.L[i]);
        this.junctionOutputR[i] = this.R[i-1] - w;
        this.junctionOutputL[i] = this.L[i] + w;

from 2.5.2 Physical Modelling of the Vocal Tract with the 2D Digital Waveguide Mesh by Jack Mullen，
I get a different function:
w= r * (this.R[i-1] - this.L[i]);
this.junctionOutputR[i] = this.R[i-1] + w;
how I got function as follows:

junctionOutputR[i] is the combine of transparent of R[i-1](wave come from A[i-1] to A[i]) and the reflection of L[i](reflection of wave L[i] from A[i] to A[i-1] ),as follows