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Grid Axes

Grid axes are defined by selecting parameters at the PARS prompt. For example, 2,3 defines a 2 dimensional parameter grid whose first (ie. x) axis is model parameter 2, and its second (ie. y) axis is model parameter 3. Unless model parameter 1 has been frozen by the user, it will be reoptimised by SGRID at every grid point.

The parameter range for each grid axis is specified by choosing an upper and lower axis range in standard ASTERIX ranges format. The selected range must fall within the valid range of the parameter within the model file - if it does not then it is truncated to that range. The spacing of points along each grid axis may be either linear or logarithmic. The OPT parameter controls how this is specified -

   OPT = 1     All axes are linearly spaced
   OPT = 2     All axes are linearly spaced in log(parameter value)
   OPT = 3     User chooses from linear/logarithmic for each axis
               using the LOG1..7 parameters.

The default for OPT is 1.

An improvement to choosing default axis ranges from allowed range of parameter value is choose the current error bounds. This feature can be enabled by specifying the ERR keyword on the command line. This assumes that sensible error values are present in the model dataset, ie. that one of SFIT/SERROR has already been run.

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