program to calculate Ybus using Singular Transformation

Reference: Power System Engineering - Nagrath Kothari| Page 195| Example 6.2

SINGULAR TRANSFORMATION (Ybus = A' y A)
    A(no. of bus x no. of element) = Bus incidence matrix
    y(no. of element x no. of element) = primitive admittance matrix
    A' = Transpose of Bus Incidence Matrix
    
    Reference: Power System Engineering - Nagrath Kothari
    Page 195
    Example 6.2
    ----------------------------------
    Line bus    |   R pu    |   X pu
    to bus      |           |   
    ----------------------------------
    1 - 2       |   0.05    |   0.15
    1 - 3       |   0.10    |   0.30
    2 - 3       |   0.15    |   0.45
    2 - 4       |   0.10    |   0.30
    3 - 4       |   0.05    |   0.15
    ----------------------------------