friction coefficient between different materials

Hi, there are two kinds of sphere with different materials. The inner friction angle of the two kinds are 10 and 20 respectively. If the coefficient of friction between the two kinds of sphere is tan15, how could I set this value?

### Matrix
Density1 = 2600
PoissonRatio1 = 0.5
frictionangle1 = 10
Young1 = 10e7
Num1 = 9000

### Filler
Density2 = 3000
PoissonRatio2 = 0.5
frictionangle2 = 20
Young2 = 10e7
Num2 = 8

Damp = 0.25

#Packing variables
Size = 0.05
mn = Vector3(0, 0, 0)
mx = Vector3(Size, Size, Size)

mat1 = O.materials.append(FrictMat(young=Young1,poisson=PoissonRatio1,frictionAngle=radians(frictionangle1),density=Density1,label='Matrix'))
mat2 = O.materials.append(FrictMat(young=Young2,poisson=PoissonRatio2,frictionAngle=radians(frictionangle2),density=Density2,label='Filler'))

sp = pack.SpherePack()
sp.makeCloud(minCorner=mn, maxCorner=mx, rMean=0.0001, rRelFuzz=0, num=Num1, distributeMass = False, periodic = False)
sp.makeCloud(minCorner=mn, maxCorner=mx, rMean=0.0005, rRelFuzz=0, num=Num2, distributeMass = False, periodic = False)
sp.toSimulation()

for b in O.bodies:
    if isinstance(b.shape,Sphere):
        if b.shape.radius==0.0001:
            b.shape.color = (0, 0, 1)
            b.mat=O.materials[mat1]

for c in O.bodies:
    if isinstance(c.shape,Sphere):
        if c.shape.radius==0.0005:
            c.shape.color = (0, 0, 1)
            c.mat=O.materials[mat2]