fix bug 282: add the possibiliry to shift the diagonal coefficients via a linear function.
fix bug 282: add the possibiliry to shift the diagonal coefficients via a linear function.

cjntaylor/eigen,cjntaylor/eigen,cjntaylor/eigen,pthulhu/eigen,pthulhu/eigen,pthulhu/eigen,cjntaylor/eigen,pthulhu/eigen,pthulhu/eigen