The function histograms_2d() records two dimensional
histograms of pairs of fields. The file parameters.h contains
an array that lists the pairs for which these histograms are to be
calculated, as well as two parameters giving the number of bins to use
in each direction. The basic structure of this function is similar to
histograms(). The minimum and maximum value used in each histogram are given by the parameters histogram2d_min and histogram2d_max or, if these are equal, set dynamically to the minimum and maximum value of each field at that time. Next the bin values are fixed in a two dimensional
array between those limiting values. Then the number of grid points in
each square of that array is counted. The file
histogram2dtimes_ext is similar to histogramtimes
from the histogram() function except that for each
histogram the file now lists the minimum value of the first field, the
bin spacing of the first field, and then the minimum value and bin
spacing of the second field. The files
histogram2dfield1_number
_
field2_number
_ext
lists the bin frequencies in a single column. They should be read in
the usual C array order. In other words if the histogram has
bins
in the second field direction then the first
frequencies
represent increasing values of the second field with the first field
at its minimum, the next
represent increasing values of the
second field with the first field at its next highest value, and so
forth.