The name of the files = synthXXXK.txt
 
They are plain ascii files that define synthetic pillar grids.
Their structure is as follows:
- The first line is the dimensions Ni*Nj*Nk of the grid and its size along the x- and y-axis.
- Followed by serveral level functions and crack functions.


Available level functions are:
 - z = level defined by 'const level'
 - z = beta * cos( alpha * x) + level defined by 'cos alpha beta level',
 - z = beta * sin( alpha * x) + level defined by 'sin alpha beta level',
 - z = beta1 * cos( alpha1 * x) + beta2 * sin( alpha2 * y) + level defined by 'cossin alpha1 beta1 alpha2 beta2 level'.


Available crack functions are:
 - z = z + offset if i < Ni * a defined by 'stepicrack a offset' with 0 < a < 1
 - z = z + offset if j < Nj * a defined by 'stepjcrack a offset' with 0 < a < 1 
 - z = z + offset if b * i + Nj * a < j defined by 'linearcrack a b offset' with 0 < a < 1 
 