1 /* vnorm.f -- translated by f2c (version 19980913).
2 You must link the resulting object file with the libraries:
3 -lf2c -lm (in that order)
4 */
5
6 #include "f2c.h"
7
8 /* $Procedure VNORM ( Vector norm, 3 dimensions ) */
vnorm_(doublereal * v1)9 doublereal vnorm_(doublereal *v1)
10 {
11 /* System generated locals */
12 doublereal ret_val, d__1, d__2, d__3;
13
14 /* Builtin functions */
15 double sqrt(doublereal);
16
17 /* Local variables */
18 doublereal v1max;
19
20 /* $ Abstract */
21
22 /* Compute the magnitude of a double precision, 3-dimensional */
23 /* vector. */
24
25 /* $ Disclaimer */
26
27 /* THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE */
28 /* CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. */
29 /* GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE */
30 /* ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE */
31 /* PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" */
32 /* TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY */
33 /* WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A */
34 /* PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC */
35 /* SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE */
36 /* SOFTWARE AND RELATED MATERIALS, HOWEVER USED. */
37
38 /* IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA */
39 /* BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT */
40 /* LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, */
41 /* INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, */
42 /* REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE */
43 /* REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. */
44
45 /* RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF */
46 /* THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY */
47 /* CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE */
48 /* ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. */
49
50 /* $ Required_Reading */
51
52 /* None. */
53
54 /* $ Keywords */
55
56 /* VECTOR */
57
58 /* $ Declarations */
59 /* $ Brief_I/O */
60
61 /* VARIABLE I/O DESCRIPTION */
62 /* -------- --- -------------------------------------------------- */
63 /* V1 I Vector whose magnitude is to be found. */
64
65 /* $ Detailed_Input */
66
67 /* V1 This may be any 3-dimensional, double precision vector. */
68
69 /* $ Detailed_Output */
70
71 /* VNORM is the magnitude of V1 calculated in a numerically stable */
72 /* way. */
73
74 /* $ Parameters */
75
76 /* None. */
77
78 /* $ Particulars */
79
80 /* VNORM finds the component of V1 whose magnitude is the largest. */
81 /* If the absolute magnitude of that component indicates that a */
82 /* numeric overflow would occur when it is squared, or if it */
83 /* indicates that an underflow would occur when square (giving a */
84 /* magnitude of zero) then the following expression is used: */
85
86 /* VNORM = V1MAX * MAGNITUDE OF [ (1/V1MAX)*V1 ] */
87
88 /* Otherwise a simpler expression is used: */
89
90 /* VNORM = MAGNITUDE OF [ V1 ] */
91
92 /* Beyond the logic described above, no further checking of the */
93 /* validity of the input is performed. */
94
95 /* $ Examples */
96
97 /* The following table show the correlation between various input */
98 /* vectors V1 and VNORM: */
99
100 /* V1 VNORM */
101 /* ----------------------------------------------------------------- */
102 /* (1.D0, 2.D0, 2.D0) 3.D0 */
103 /* (5.D0, 12.D0, 0.D0) 13.D0 */
104 /* (-5.D-17, 0.0D0, 12.D-17) 13.D-17 */
105
106 /* $ Restrictions */
107
108 /* None. */
109
110 /* $ Exceptions */
111
112 /* Error free. */
113
114 /* $ Files */
115
116 /* None. */
117
118 /* $ Author_and_Institution */
119
120 /* W.M. Owen (JPL) */
121
122 /* $ Literature_References */
123
124 /* None. */
125
126 /* $ Version */
127
128 /* - SPICELIB Version 1.0.1, 10-MAR-1992 (WLT) */
129
130 /* Comment section for permuted index source lines was added */
131 /* following the header. */
132
133 /* - SPICELIB Version 1.0.0, 31-JAN-1990 (WMO) */
134
135 /* -& */
136 /* $ Index_Entries */
137
138 /* norm of 3-dimensional vector */
139
140 /* -& */
141
142 /* Determine the maximum component of the vector. */
143
144 /* Computing MAX */
145 d__1 = abs(v1[0]), d__2 = abs(v1[1]), d__1 = max(d__1,d__2), d__2 = abs(
146 v1[2]);
147 v1max = max(d__1,d__2);
148
149 /* If the vector is zero, return zero; otherwise normalize first. */
150 /* Normalizing helps in the cases where squaring would cause overflow */
151 /* or underflow. In the cases where such is not a problem it not worth */
152 /* it to optimize further. */
153
154 if (v1max == 0.) {
155 ret_val = 0.;
156 } else {
157 /* Computing 2nd power */
158 d__1 = v1[0] / v1max;
159 /* Computing 2nd power */
160 d__2 = v1[1] / v1max;
161 /* Computing 2nd power */
162 d__3 = v1[2] / v1max;
163 ret_val = v1max * sqrt(d__1 * d__1 + d__2 * d__2 + d__3 * d__3);
164 }
165
166 return ret_val;
167 } /* vnorm_ */
168
169