1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
*DECK ISAMAX
INTEGER FUNCTION ISAMAX (N, SX, INCX)
C***BEGIN PROLOGUE ISAMAX
C***PURPOSE Find the smallest index of that component of a vector
C having the maximum magnitude.
C***LIBRARY SLATEC (BLAS)
C***CATEGORY D1A2
C***TYPE SINGLE PRECISION (ISAMAX-S, IDAMAX-D, ICAMAX-C)
C***KEYWORDS BLAS, LINEAR ALGEBRA, MAXIMUM COMPONENT, VECTOR
C***AUTHOR Lawson, C. L., (JPL)
C Hanson, R. J., (SNLA)
C Kincaid, D. R., (U. of Texas)
C Krogh, F. T., (JPL)
C***DESCRIPTION
C
C B L A S Subprogram
C Description of Parameters
C
C --Input--
C N number of elements in input vector(s)
C SX single precision vector with N elements
C INCX storage spacing between elements of SX
C
C --Output--
C ISAMAX smallest index (zero if N .LE. 0)
C
C Find smallest index of maximum magnitude of single precision SX.
C ISAMAX = first I, I = 1 to N, to maximize ABS(SX(IX+(I-1)*INCX)),
C where IX = 1 if INCX .GE. 0, else IX = 1+(1-N)*INCX.
C
C***REFERENCES C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
C Krogh, Basic linear algebra subprograms for Fortran
C usage, Algorithm No. 539, Transactions on Mathematical
C Software 5, 3 (September 1979), pp. 308-323.
C***ROUTINES CALLED (NONE)
C***REVISION HISTORY (YYMMDD)
C 791001 DATE WRITTEN
C 861211 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900821 Modified to correct problem with a negative increment.
C (WRB)
C 920501 Reformatted the REFERENCES section. (WRB)
C 920618 Slight restructuring of code. (RWC, WRB)
C***END PROLOGUE ISAMAX
REAL SX(*), SMAX, XMAG
INTEGER I, INCX, IX, N
C***FIRST EXECUTABLE STATEMENT ISAMAX
ISAMAX = 0
IF (N .LE. 0) RETURN
ISAMAX = 1
IF (N .EQ. 1) RETURN
C
IF (INCX .EQ. 1) GOTO 20
C
C Code for increment not equal to 1.
C
IX = 1
IF (INCX .LT. 0) IX = (-N+1)*INCX + 1
SMAX = ABS(SX(IX))
IX = IX + INCX
DO 10 I = 2,N
XMAG = ABS(SX(IX))
IF (XMAG .GT. SMAX) THEN
ISAMAX = I
SMAX = XMAG
ENDIF
IX = IX + INCX
10 CONTINUE
RETURN
C
C Code for increments equal to 1.
C
20 SMAX = ABS(SX(1))
DO 30 I = 2,N
XMAG = ABS(SX(I))
IF (XMAG .GT. SMAX) THEN
ISAMAX = I
SMAX = XMAG
ENDIF
30 CONTINUE
RETURN
END
|
