def Area_triangle(nodes):
    """
    A function to calculate the area for a triangular element
    input: nodal coordinates of the 3 nodes
    """
    x1 = nodes[0,0]
    y1 = nodes[0,1]
    x2 = nodes[1,0]
    y2 = nodes[1,1]
    x3 = nodes[2,0]
    y3 = nodes[2,1]
    A = 0.5*((x2-x1)*(y3-y1)-(x3-x1)*(y2-y1))
    #A = 0.5*((x2*y3-x3*y2)+(y2-y3)*x1+(x3-x2)*y1)
    return A