# Parameter error analysis

## Relax-fit script mode - error analysis for parameters

Only one technique adequately estimates parameter errors when the parameter values where found by optimisation - Monte Carlo simulations.

In relax this can be implemented by using a series of functions from the monte_carlo user function class.

Firstly the number of simulations needs to be set

monte_carlo.setup(number=500)

For each simulation, randomised relaxation curves will be fit using exactly the same methodology as the original exponential curves.

These randomised curves are created by back calculation from the fitted model parameter values and then each point on the curve randomised using the error values set earlier in the script

monte_carlo.create_data()

As a grid search for each simulation would be too computationally expensive, the starting point for optimisation for each simulation can be set to the position of the optimised parameter values of the model

monte_carlo.initial_values()

Then exactly the same optimisation as was used for the model can be performed

minimise(`simplex', constraints=False)

The parameter errors are then determined as the standard deviation of the optimised parameter values of the simulations

monte_carlo.error_analysis()