Data Analysis ||
Data files for some examples
Example pages containing:
Probability Distribution Functions
The probability distribution (frequency of occurrence) of an individual
, may be obtained via the
Given two variables X
, the bivariate
joint probability distribution returned by the pdfxy
function indicates the probability of occurrence defined in terms of both X
Generally, the larger the array(s) the smoother the derived PDF.
Bin sizes of less-than [greater-than] the default number of 25 bins will
result in smoother [rougher] plots.
Using the pdfx
this example illustrates univariate PDFs from three
variables with three different distributions.
Default settings of parameters are used (eg.
, 25 bins).
This illustrates using a user specified number of bins.
Here, 40 bins are specified. This results in a more ragged
view of the distribution.
Use of the returned bin_center
attributes from three PDFs to place all on
a common x-axis is illustrated. (Minor changes would be required if
the number of bins used had been different.)
illustrate using a bar style plot.
Using the pdfxy
illustrate a simple bivariate PDF using two variables having normal
Similar to Example 3 but use different bin numbers.
Given a fixed number of values, the fewer bins used, the smoother
the resulting PDF.
The bivariate distributions of variables from variables with different
univariate distributions will yield different patterns.
Here, the univariate distributions of Example 1 are used
to create bivariate PDFs.
Some tuning of plots may be necessary to focus on regions of interest.
Here, the "Gamma/Chi" distributions are highly skewed. There are
large areas where the joint probabilites are near or at zero.
NCL coordinate subscripting is used to select regions of interest.
Variables that may not be continuous [probabilities=0.0]
may be best viewed via use of "raster" plots. These clearly show
the bin and data resolution.
Note that using gsn_csm_contour results in
the raster bins at the edges being reduced to half width. The use of
plt_pdfxy located in the shea_util expands the
contour area and allows the edge raster bins to be fully viewed.