We want to provide a collection of layers where the material properties changes from those of the uppermost layer to those of the lowermost layer.

Initially we are

• using a linear interpolation to change the properties.
• allowing the user to specify how many discrete layers that should be used.
• when optimizing the structure the thickness of each of the discrete layers should be changed in a concerted way.
• the thickness of the gradient layer is given by the number of layers multiplied with the layer thickness