gtsam
3rdparty
GeographicLib
java
src
main
java
net
sf
geographiclib
Accumulator.java
Go to the documentation of this file.
1
8
package
net.sf.geographiclib;
9
25
public
class
Accumulator
{
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// _s + _t accumulators for the sum.
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private
double
_s
, _t;
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public
Accumulator
(
double
y
) {
_s
=
y
; _t = 0; }
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public
Accumulator
(
Accumulator
a
) {
_s
=
a
._s; _t =
a
._t; }
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public
void
Set
(
double
y
) {
_s
=
y
; _t = 0; }
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public
double
Sum
() {
return
_s
; }
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public
double
Sum
(
double
y
) {
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Accumulator
a
=
new
Accumulator
(
this
);
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a
.Add(
y
);
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return
a
._s;
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}
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public
void
Add
(
double
y
) {
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// Here's Shewchuk's solution...
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double
u;
// hold exact sum as [s, t, u]
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// Accumulate starting at least significant end
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{
Pair
r =
GeoMath
.
sum
(
y
, _t);
y
= r.
first
; u = r.
second
; }
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{
Pair
r =
GeoMath
.
sum
(
y
,
_s
);
_s
= r.
first
; _t = r.
second
; }
75
// Start is _s, _t decreasing and non-adjacent. Sum is now (s + t + u)
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// exactly with s, t, u non-adjacent and in decreasing order (except for
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// possible zeros). The following code tries to normalize the result.
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// Ideally, we want _s = round(s+t+u) and _u = round(s+t+u - _s). The
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// following does an approximate job (and maintains the decreasing
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// non-adjacent property). Here are two "failures" using 3-bit floats:
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//
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// Case 1: _s is not equal to round(s+t+u) -- off by 1 ulp
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// [12, -1] - 8 -> [4, 0, -1] -> [4, -1] = 3 should be [3, 0] = 3
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//
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// Case 2: _s+_t is not as close to s+t+u as it shold be
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// [64, 5] + 4 -> [64, 8, 1] -> [64, 8] = 72 (off by 1)
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// should be [80, -7] = 73 (exact)
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//
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// "Fixing" these problems is probably not worth the expense. The
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// representation inevitably leads to small errors in the accumulated
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// values. The additional errors illustrated here amount to 1 ulp of the
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// less significant word during each addition to the Accumulator and an
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// additional possible error of 1 ulp in the reported sum.
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//
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// Incidentally, the "ideal" representation described above is not
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// canonical, because _s = round(_s + _t) may not be true. For example,
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// with 3-bit floats:
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//
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// [128, 16] + 1 -> [160, -16] -- 160 = round(145).
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// But [160, 0] - 16 -> [128, 16] -- 128 = round(144).
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//
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if
(
_s
== 0)
// This implies t == 0,
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_s
= u;
// so result is u
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else
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_t += u;
// otherwise just accumulate u to t.
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}
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public
void
Negate
() {
_s
= -
_s
; _t = -_t; }
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}
net.sf.geographiclib.Pair.second
double second
Definition:
Pair.java:23
net.sf.geographiclib.GeoMath.sum
static Pair sum(double u, double v)
Definition:
GeoMath.java:135
net.sf.geographiclib.Accumulator.Sum
double Sum(double y)
Definition:
Accumulator.java:59
net.sf.geographiclib.Accumulator.Sum
double Sum()
Definition:
Accumulator.java:51
net.sf.geographiclib.Accumulator
Definition:
Accumulator.java:25
net.sf.geographiclib.Accumulator.Accumulator
Accumulator(Accumulator a)
Definition:
Accumulator.java:39
net.sf.geographiclib.Pair.first
double first
Definition:
Pair.java:19
net.sf.geographiclib.Accumulator.Add
void Add(double y)
Definition:
Accumulator.java:69
net.sf.geographiclib.Pair
Definition:
Pair.java:15
y
Scalar * y
Definition:
level1_cplx_impl.h:124
net.sf.geographiclib.Accumulator.Negate
void Negate()
Definition:
Accumulator.java:112
a
ArrayXXi a
Definition:
Array_initializer_list_23_cxx11.cpp:1
net.sf.geographiclib.GeoMath
Definition:
GeoMath.java:16
net.sf.geographiclib.Accumulator.Accumulator
Accumulator(double y)
Definition:
Accumulator.java:33
net.sf.geographiclib.Accumulator._s
double _s
Definition:
Accumulator.java:27
net.sf.geographiclib.Accumulator.Set
void Set(double y)
Definition:
Accumulator.java:45
gtsam
Author(s):
autogenerated on Fri Nov 1 2024 03:31:51