2 # Use this function to fit sound velocity data as function of
3 # sound propagation direction, indicated by its angle against the
4 # z-axis of an hexagonal symmetry coordinate system
6 # Adjustable parameters:
8 # c33, c11, c13, c44 elastic moduli - materials constants
11 # HBB 970522: factored out common factor 1e9 from c?? into the
12 # function, to improve the fit convergence. Fit parameters were
13 # just too grossly different before.
15 rho = 1000.0 # density in kg/m3
17 phi(x) = (x - phi0)/360.0*2.0*pi
19 main(x) = c11*sin(phi(x))**2 + c33*cos(phi(x))**2 + c44
20 mixed(x) = sqrt( ((c11-c44)*sin(phi(x))**2 \
21 +(c44-c33)*cos(phi(x))**2)**2 \
22 +(2.0*(c13+c44)*sin(phi(x))*cos(phi(x)))**2 )
24 vlong(x) = sqrt(1.0/2.0/rho*1e9*(main(x) + mixed(x)))
25 vtrans(x) = sqrt(1.0/2.0/rho*1e9*(main(x) - mixed(x)))
27 # When we read the file in, we set y=index, and we use
28 # y in this (pseudo) 3d fit to choose an x function
30 f(x,y) = y==1 ? vlong(x) : vtrans(x)