*search_grid* - Grid of $\chi ^{2}$ - default mode

After the best fit is obtained, the confidence limits on two parameters can be obtained by running search_grid. This task calculates a grid of $\chi ^{2}$ values for a given input model. The task will also calculate the absolute minimum [within the limits of the grid or the limits from the input model spectrum, whichever is larger], and use it to draw the contours ( $\chi^2_{min}$+ $\Delta\chi^{2}$).

In the simplest case the user can hit <cr> at the first few prompts. Then search_grid will select the last dataset used (from pkgpars), will use the best fit from the last run of fit (the null string ``'' at the model prompt will always select the best fit from the _prd.tab file), and will place the results in a _grd.tab file with the same root as the observed file. A grid will be built around those values, incrementing out to $\pm$ delta (provided by the user) in n_x steps in the x dimension and n_y steps in the y dimension (n_x and n_y provided by the user). search_grid will return $n_x \times n_y$$\chi ^{2}$ values, a $\chi^2_{min}$ on the grid points, and a true minimum (which will coincide with the central grid point in this simple case).

input files: rp90_prd.tab; rp90_obs.tab

output file: rp90_a_grd.tab

  xs> search_grid
  Performing a grid search.
  observed spectrum [root_obs.tab] = (rp90):  <cr>
                                                    # input data from rp90_obs.tab
  model descriptor [null --> last best fit]:  <cr>                  # The best fit
                                                # parameters are from rp90_prd.tab
  root name for output file [root_grd.tab]:  rp90_a
                                         # output is rp90_a_grd.tab.  Root changed
         # because you will probably want to repeat this with different parameters

The best-fit model parameters (from previous fit) will be listed on the screen.

Please choose the grid axes:

  model component number for the first axis (1): <cr>
  first axis parameter (norm|index|temp|galacticNh|intrinsicNh):  temp
  half range of first axis parameter:  0.5
  number of steps in the first axis (1:):  10
  model component number for the second axis (1):  2
  second axis parameter (norm|index|temp|galacticNh|intrinsicNh):  temp
  half range of second axis parameter:  0.5
  number of steps in the second axis (1:): 10

The best-fit parameters from this current grid of fits will be listed on the screen.

The output file is in table format, and can be listed with the tables.ttools task tprint.