cgloggen.pro
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; docformat = 'rst'
;
; NAME:
; cgLogGen
;
; PURPOSE:
; This function creates an evenly spaced vector of points in log space.
;
;******************************************************************************************;
; ;
; Copyright (c) 2012, by Fanning Software Consulting, Inc. All rights reserved. ;
; ;
; Redistribution and use in source and binary forms, with or without ;
; modification, are permitted provided that the following conditions are met: ;
; ;
; * Redistributions of source code must retain the above copyright ;
; notice, this list of conditions and the following disclaimer. ;
; * Redistributions in binary form must reproduce the above copyright ;
; notice, this list of conditions and the following disclaimer in the ;
; documentation and/or other materials provided with the distribution. ;
; * Neither the name of Fanning Software Consulting, Inc. nor the names of its ;
; contributors may be used to endorse or promote products derived from this ;
; software without specific prior written permission. ;
; ;
; THIS SOFTWARE IS PROVIDED BY FANNING SOFTWARE CONSULTING, INC. ''AS IS'' AND ANY ;
; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES ;
; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT ;
; SHALL FANNING SOFTWARE CONSULTING, INC. BE LIABLE FOR ANY DIRECT, INDIRECT, ;
; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED ;
; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ;
; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ;
; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ;
; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS ;
; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ;
;******************************************************************************************;
;
;+
; This function creates an evenly spaced vector of points in log space.
;
; :Categories:
; Math, Utilities
;
; :Returns:
; A vector of values, evenly spaced along a log axis.
;
; :Params:
; numpts: in, optional, type=integer, default=10
; The number of points desired in the output vector.
;
; :Keywords:
; double: in, optional, type=boolean, default=0
; Set this keyword to return the values as double precision values.
; Otherwise, floating point values are returned.
; finish: in, optional, type=float/double, default=100
; The ending value of the vector. The output values are evenly spaced
; between `Start` and `Finish`. This value must be a positive number.
; start: in, optional, type=float/double, default=1
; The starting value of the vector. The output values are evenly spaced
; between `Start` and `Finish`. This value must be a positive number.
;
; :Examples:
; To create 10 values evenly spaced between 5 and 15::
; points = cgLogGen(10, Start=5, Finish=150)
; cgPlot, points, PSym=2, /YLog
;
; :Author:
; FANNING SOFTWARE CONSULTING::
; David W. Fanning
; 1645 Sheely Drive
; Fort Collins, CO 80526 USA
; Phone: 970-221-0438
; E-mail: david@idlcoyote.com
; Coyote's Guide to IDL Programming: http://www.idlcoyote.com
;
; :History:
; Change History::
; Written, 17 January 2012. DWF.
;
; :Copyright:
; Copyright (c) 2012, Fanning Software Consulting, Inc.
;-
FUNCTION cgLogGen, numpts, $
Double=double, $
Finish=finish, $
Start=start
Compile_Opt idl2
; Error handling. Return to caller.
On_Error, 2
; Check parameters.
SetDefaultValue, numpts, 10
SetDefaultValue, finish, 100
SetDefaultValue, start, 1
SetDefaultValue, double, 0, /Boolean
; Make sure values are positive.
IF start LE 0 THEN Message, 'The starting value for the vector must be a positive value.'
IF finish LE 0 THEN Message, 'The ending value for the vector must be a positive value.'
; Compute the logarithms of the end points.
s = ALog10(start)
f = ALog10(finish)
; Create a vector of exponent values between these two end points.
exponents = cgScaleVector(Findgen(numpts), s, f, Double=double)
; Return the actual values.
RETURN, 10.^exponents
END