# How to transform a Monte Carlo PDF set into a Hessian PDF set

A Monte Carlo PDF set can be transformed into a Hessian PDF using the
method described in [CFKR16] a runcard like the one
below. In this example `Neig`

are the number of basis eigenvectors of
the Hessian PDF and `mc2hname`

is an optional argument that can be
added to give a custom name to the Hessian PDF set, if `mc2hname`

is
not defined, a default name will automatically be given to the Hessian
PDF set. By default `installgrids`

is `False`

, by setting it to
`True`

we make sure that the Hessian PDF is added to the LHAPDF
folder.

```
pdf: NNPDF31_nlo_as_0118
Neig: 100 # Number of basis eigenvectors of the Hessian PDF set
Q: 10 # Energy scale at which the MC PDF set is sampled
mc2hname: MyHessianPDF # Name of the Hessian PDF set
installgrid: True
actions_:
- mc2hessian
```