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HISTO <data>,<variable>,L
GHISTO <data>,<variable>,L  / for graphic screen
forms the frequency distribution and plots the histogram of <variable> 
in <data> according to a classification given by
  <variable>=<lower limit>(<step>)<upper limit> 

L (optional parameter) is the first line for the table of the frequency
distribution. The results are saved also in an output file, if that is
specified (see OUTPUT).
Furthermore the frequency distribution is saved in file FREQ.F on
the data disk and it can be used later by a HISTO operation of the form
HISTO data>F,<variable>,L.
Especially histograms of large data files are replotted faster by this
option thus permitting fitting of various theoretical distributions to
the same frequency distribution (see FIT below).

Example: HISTO DATA1,Weight  / Weight=40(2)100
         Classes of Weight will be  1: 40<Weight<=42
                                    2: 42<Weight<=44
                                   30: 98<Weight<=100
Various theoretical distributions may be fitted and the corresponding
frequency curve is plotted on the histogram by using a specification
of the form FIT=<name of the distribution>.
The following distributions are available:
NORMAL(mean,variance)       X is N(mean,variance)
LOGNORMAL(mean,variance)    log X is N(mean,variance)
UNIFORM(a,b)                X has uniform distribution on (a,b)
BINOMIAL(N,p)               X is Bin(N,p)
POISSON(mean)               X is Poisson(mean)

The user may also define his/her own distribution (see below).

If the parameters of the distribution are not given, the maximum
likelihood estimates computed from the frequency distribution are
used. Examples: FIT=NORMAL(175,36.5)  FIT=NORMAL
If FIT is used, the results will also include the fitted frequencies and
the common Chi-square test. In this test consecutive classes are com-
bined when necessary to meet the condition
       expected frequency >= min
where <min> is given by MINF=<min>. Default is MINF=5.

When using FIT for discrete distributions the <variable> specification
must be of the form <variable>=-0.5(1)<max.value+0.5>.

In continuous distributions, theoretical frequencies are computed by
numerical integration using a step length <step>/2. To replace this
by <step>/K, a specification STEPDIVISOR=K must be given.

Other extra specifications of HISTO are
being mostly the same as those of the PLOT operation for scatter
The bars in the histogram are filled with the shading [FILL1] defined
in the current plotting driver. Redefinition like [FILL1]=[FILL4] is
allowed in the HISTO scheme. By FILL=NO bars are not filled at all.
In PostScript plotting the color for bars can be selected, for example,
by setting [FILL-1]=1,1,0.5,0 (cmyk components) FILL=-1 .

By default, an error message is given if no observations are
accepted. This message is removed by ACCEPT=0.
Also an error message appears when all observations belong to the
same class. This message is removed by ACCEPT=1 (or ACCEPT=0).

  U = User-defined distributions for HISTO 
  S = Information on scatter diagrams 

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