Y201 Find Histogram-Channel

IUCHAN, IUBIN, IUHIST all find the histogram-channel for a given quantity in the same way. They differ only slightly in the way in which the parameters are passed.

Structure:

FUNCTION subprograms
User Entry Names: IUCHAN, IUBIN, IUHIST

Usage:

All routines need the the following parameters:

X

( REAL) Quantity to be histogrammed.

XLOW

( REAL) Lower limit of the histogram.

DX

( REAL) Channel width.

NX

( INTEGER) Number of channels.

$\epsilon >\; 0$ is a small bias to counteract rounding effects when X is exactly on a bin edge, a likely and serious problem when compressed data are histogrammed.

$\epsilon =\; 10-5$ on 32-bit machines, $\epsilon =\; 10-6$ on machines with a larger word size.
Function IUCHAN:

    N = IUCHAN(X,XLOW,DX,NX)

Functions IUBIN and IUHIST:

    DIMENSION PAR(3)
    EQUIVALENCE(NX,PAR(1))
    LOGICAL SPILL
 
    N = IUBIN (X,PAR,SPILL)
    N = IUHIST(X,PAR,SPILL)

PAR

Histogram parameters:
$PAR(1)\; \equiv NX$
$PAR(2)\; \equiv DX$ (for IUBIN), or $\equiv 1/DX$ reciprocal of the channel width (for IUHIST).
$PAR(3)\; \equiv XLOW$

SPILL

( LOGICAL) Flag set to .TRUE. or .FALSE. depending on whether X is outside or inside the histogram.

Y250