Welcome to the Harris Geospatial product documentation center. Here you will find reference guides, help documents, and product libraries.


  >  Docs Center  >  Libraries  >  ASTROLIB  >  RANDOMP

RANDOMP

RANDOMP

Name


      RANDOMP

Purpose


      Generates an array of random numbers distributed as a power law.

Calling Sequence


      RANDOMP, X, Pow, N, [ RANGE_X = [low,high], SEED= ]'

Inputs


      Pow: Exponent of power law.
              The pdf of X is f_X(x) = A*x^pow, low <= x <= high
              ASTRONOMERS PLEASE NOTE:
              pow is little gamma = big gamma - 1 for stellar IMFs.
      N: Number of elements in generated vector.

Optional Input Keyword Parameter


      RANGE_X: 2-element vector [low,high] specifying the range of
              output X values; the default is [5, 100].
  OPTIONAL INPUT-OUTPUT KEYWORD PARAMETER:
      SEED: Seed value for RANDOMU function. As described in the
              documentation for RANDOMU, the value of SEED is updated on
              each call to RANDOMP, and taken from the system clock if not
              supplied. This keyword can be used to have RANDOMP give
              identical results on different runs.

Outputs


      X: Vector of random numbers, distributed as a power law between
              specified range

Procedure


      "Transformation Method" for random variables is described in Bevington
      & Robinson, "Data Reduction & Error Analysis for Physical Sciences", 2nd
      Edition (McGraw-Hill, 1992). p. 83.
      Output of RANDOMU function is transformed to power-law
      random variable.

Example


      Create a stellar initial mass function (IMF) with 10000 stars
      ranging from 0.5 to 100 solar masses and a Salpeter slope. Enter:
      RANDOMP,MASS,-2.35,10000,RANGE_X=[0.5,100]

Notes


      Versions 5.1.1 and V5.2 of IDL have a bug in RANDOMU such that the SEED
      value is initialized to the same value at the start of each session,
      rather than being initialized by the system clock. RANDOMP will be
      affected in a similar manner.

Modification History


      Written by R. S. Hill, Hughes STX, July 13, 1995
      July 14, 1995 SEED keyword added at Landsman's suggestion.
                    Documentation converted to standard format. RSH
      Converted to IDL V5.0 W. Landsman September 1997



© 2018 Harris Geospatial Solutions, Inc. |  Legal
My Account    |    Store    |    Contact Us