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erfc.cpp
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Created
Fri, Sep 27, 07:47
Size
1 KB
Mime Type
text/x-c
Expires
Sun, Sep 29, 07:47 (2 d)
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blob
Format
Raw Data
Handle
21138520
Attached To
rLAMMPS lammps
erfc.cpp
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//This code was written by Philip Nicoletti
//http://www.codeguru.com/forum/archive/index.php/t-129990.html
//
//Modified by Jin Ma, Oklahoma State University for LAMMPS
//erfc() is defined in GNU libraries. This code is a simplified
//version for implementation with Visual C++.
//
//Warning: these functions are not fully tested.
//
#include "erfc.h"
#include "math.h"
double
erf
(
double
x
)
{
//
// Computation of the error function erf(x).
//
return
(
1
-
erfc
(
x
));
}
//
//
double
erfc
(
double
x
)
{
//
// Computation of the complementary error function erfc(x).
//
// The algorithm is based on a Chebyshev fit as denoted in
// Numerical Recipes 2nd ed. on p. 214 (W.H.Press et al.).
//
// The fractional error is always less than 1.2e-7.
//
//
// The parameters of the Chebyshev fit
//
const
double
a1
=
-
1.26551223
,
a2
=
1.00002368
,
a3
=
0.37409196
,
a4
=
0.09678418
,
a5
=
-
0.18628806
,
a6
=
0.27886807
,
a7
=
-
1.13520398
,
a8
=
1.48851587
,
a9
=
-
0.82215223
,
a10
=
0.17087277
;
//
double
v
=
1
;
// The return value
double
z
=
fabs
(
x
);
//
if
(
z
==
0
)
return
v
;
// erfc(0)=1
double
t
=
1
/
(
1
+
0.5
*
z
);
v
=
t
*
exp
((
-
z
*
z
)
+
a1
+
t
*
(
a2
+
t
*
(
a3
+
t
*
(
a4
+
t
*
(
a5
+
t
*
(
a6
+
t
*
(
a7
+
t
*
(
a8
+
t
*
(
a9
+
t
*
a10
)))))))));
if
(
x
<
0
)
v
=
2
-
v
;
// erfc(-x)=2-erfc(x)
return
v
;
}
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